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Potential short circuit maybe in the CAN bus

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by timglen, Jan 19, 2016.

  1. timglen

    timglen New Member

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    I purchased a 2008 prius at an auction that had issues that were not defined. The lights on the dash were:
    ABS,VSC,(!),SLIP Indicator Light (car swerving icon),check engine icon

    I bought the mini vci that came with Techstream software (version 10.00.028) and I ran it initially and found these codes:

    C1241
    C1378
    C1203
    C1345
    C1392

    I believe there is a short circuit somewhere that is making the auxiliary battery go to a low voltage after only a few minutes of testing. After I charge it with the Optima charger (recommended on priuschat) it is 13.2 volts and when the ready light is on (and the engine starts) the display shows that the HV is charging and when I attach a voltmeter to the auxiliary battery it goes up to 13.9 volts. But after about 5 minutes of running and I shut it off and the try to turn it on the ready light will not come on again and the aux battery is down to 11.5 volts. The battery was tested at a local auto parts store and they said it was fine, in fact I have an addition battery that someone gave me and it was shown to be good as well but they both go down in voltage after turning on the prius.

    I bought a used Skid Control ECU on ebay (because of the C1203 code) and installed it (very difficult) but after that there were no warnings on the display and I drove it with no issues.

    Then I ran Techstream again and did a system check and it come up with:

    U0121
    B1421
    B1794
    B1650
    B1660

    That looked good but then I ran the "CAN bus check" because I thought there might still be a short (thinking it was on the CAN bus) and then all the entries (e.g. ECM (Engine), HV Battery) stayed red (= No longer communicating on the CAN BUS).

    And also all of the lights that were on before replacing Skid Control Unit went on again:
    ABS,VSC,(!),SLIP Indicator Light (car swerving icon),check engine icon

    I ran the CAN bus check when the Ready light was on and read somewhere that you shouldn't do that so maybe that is was did the damage to either the CAN bus or the ECU's connected to it. Now I can not even get the ready light to go on.

    Anyway I have been using pdf documents that show how to track down potential short circuits but I found different values for ohms. When I measure the resistance between CANH and the Battery + using the OBD connector I get about 8K ohms but one document I have says it should be more than 1M ohm and the other says it should be more than 6K ohms (see attached screen shots).

    Has anyone every measured the resistance between pin 6 and pin 16 on the OBD connector? If so what was the resistance?
    At least it will help me direct my attention in the right direction. I have tried measuring the resistance after disconnecting all of the ECU's one at a time to see if one of them was causing the potential short circuit but there was no significant change.

    Thanks for your help!
    Tim
     

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  2. ChapmanF

    ChapmanF Senior Member

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    I think it would take a significant current draw somewhere in the car, to drag a good battery from 13.2 to 11.5 in what sounds like a short period from your description.

    I don't think I'd suspect the CAN wiring immediately, because (a) that is light gauge wiring only for communication purposes, and if it were carrying enough current to drain a battery that fast, you would probably have the smell of cooked wires; (b) that's the communication network you're using when you're reading the codes, and if it were shorted you wouldn't be succeeding in doing that.

    Unfortunately, I don't have a Gen 2 wiring diagram. In Gen 1, the power distribution section shows a peculiar design with some loads taken off each side of the 100A DC/DC fuse. In other words, in Gen 1 when that fuse is open, the electrical system gets strangely partitioned, with some things powered only by the battery (which never charges), and other things only by the converter (which shows a nice healthy charge voltage).

    I would suggest going to techinfo.toyota.com for your 2008 wiring diagram manual, and studying the power distribution section carefully for that sort of issue ... it will probably give you ideas.

    -Chap
     
  3. valde3

    valde3 Senior Member

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    Measure the current draw from 12V battery. Measure it in OFF, ACC, and IGN-ON. And if you see the current draw then you can test (first by just pulling fuses) what is drawing the current. Draw has to be pretty big to drain battery like that. If it only drains the 12V battery in ready, that’s a big clue by itself.

    I would probably use this method since random codes are many times generated with empty or faulty 12V battery and if it drains the battery like that you constantly have conditions that are similar to faulty/empty battery. If some or even all the code conditions are real probably fixing the current draw will lead you to the thing that causes all of the problems.
     
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Most digital multimeters have a fuse-protected ammeter at 10A. So if you attempt to measure IG-ON current you will probably blow the fuse.
     
  5. Dion Kraft

    Dion Kraft Member

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    I have been thinking about this since post last night. Others have chimed in with good info and suggestions.
    On a normal car we would use the DVOM and in AMP mode connect the DVOM in between the Negative cable. Start pulling each fuse to see the amount of amperage loss indicated. Write it down. Reinsert and on to the next one. Usually eventually we would arrive to the highest one and then its time to check that leg of the circuit. In this case as Mr Wong had indicated its more than 10A the fuse in the DVOM will blow but as long as you have a fuse you might try it once. The other strategy is to pull the fuse while the eng system is on and while its in its discharge of 12v battery mode. Lastly you can pull the fuse or a fuse and get the car in the discharge state and see what effect that has on the voltage run down. Can't think of anything else at this juncture.
     
  6. ChapmanF

    ChapmanF Senior Member

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    For larger currents, it's possible to use a clamp-on current sensor. The basic, purely inductive kind are not so useful on cars because they can only measure AC, but the Hall-effect kind, for a bit more money, will measure DC. The one I have puts out a voltage proportional to the measured current, one millvolt per amp, so you just plug it into a meter that is set on mV, and read the display as if it were amps.

    In my experience it's not great for small currents (anything below 3 or 4 amps kind of gets lost in the uncertainty, improves a little bit if I clamp on both ways, then average the absolute values) ... but then, if the clamp shows you the current is that low, you know you'd be able to measure directly.

    -Chap
     
  7. Patrick Wong

    Patrick Wong DIY Enthusiast

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    I think the OP should make the Prius READY and put a voltmeter on the 12V bus. Confirm that the voltage reading is 13.8V. Then leave the Prius READY for a long time, and see whether the voltage remains at 13.8V or not.

    If the voltage starts to drop as time passes, I think it is more likely that there is a problem with the DC/DC converter within the inverter overheating and no longer producing voltage, and the inverter would need to be replaced.

    In addition, the skid control ECU has a problem with communications which may be associated with an intermittent wiring harness problem. I doubt that the comm issue is causing the drop in voltage, as Chap already mentioned.
     
  8. edthefox5

    edthefox5 Senior Member

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    We see alot of these. Auction buys.

    Recurring vsc infers wheel sensor issue. Since auction buy was probably plowed hard somewhere on the chassis and has wheel/suspension/wiring damage and was repaired poorly. With all those skid control nags your brakes must be bad too?

    Whats not right is I don't see any Hybrid codes being thrown. If the can buss bean was damaged the car would be in a world of hurt and you'd be throwing gateway nags. So somethings not right with your mini diagnosis.

    With any 12 volt issues on this car replace the 12 volt immediately. Can't tell you how many people come on here swearing there 12 volt is good with obvious 12 volt issues. Replace battery first. Then pull every fuse in the car and check it out of circuit.

    Then go on toyota.com/owners and join. List the cars vin and see how many times its been to a toyota dealer and for what. All dealer events for the life of the car will be listed there. You may find some interesting info on there concerning this event. Lots of people blow there Prius up and then after the dealer gives them a $4000 estimate they trade it in on the spot. Dealer rolls it to the auction then next stop your house.

    If it was me I would go to the dealer and spend $100 and have them pull a Techstream session on the car as your mini is not reporting all the events correctly imho.
     
  9. timglen

    timglen New Member

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    Thank you all for your suggestions!

    It makes sense that a short in the CAN bus would not be enough to drain the battery, so I will not look for shorts in the CAN bus anymore, good tip.

    I wanted to confirm some volt/amp measurements that I had done in the past so last night I ran them.
    I bought a bayite DC 6.5-100V 0-100A LCD on amazon and have been using for some time it but I am not sure how accurate it is, any thought on this?
    In the past if I pressed the brake pedal and hit the power button the current meter would start flashing, I am guessing that is was above the 100 amp limit of the meter.

    So I did some tests last night.
    When I pushed the button twice (w/o brake), there was clicking coming from the engine, when I heard the clicking sound the amps would go up to over 20 but when it stopped the amps would go down to about 8 but after some time it stopped clicking.

    Here are the results:
    Power button Volts Amps
    off 12.7 .86 with key inserted, w/o key .00? (meter only has 2 digits)
    push once 12.6 1.38
    push twice 12.3 8

    I am charging my new optima battery (using the optima charger) now and will install it soon and run the tests again because I ran techstream and got the code C1241 (and C1242) and I also had the red triangle when I did these tests. It looks like this battery is too low so I don't know if it causes some of the other error codes I got:
    U0100, U0293, U0123, U0124, U0273, B1650, B1660.

    But it did do something that I have not see before which is when I stepped on the brake and hit the power button, the ready light would go on and the engine would start but then after a few second both would stop. I am hoping it is just because of the low battery.

    As for the brakes, I have driven it a few times. I drove it from the auction but we had to have a second aux battery connected with jumper cables to the main aux battery. I don't remember having any brake problems but I should probably have them inspected, and probably should take it to the local dealer for a complete techstream test. I didn't know anything about toyota-com-owners, thanks for that tip!

    Patrick, I believe in the past when I was able to get the engine running for some time the voltage on the aux battery was 13.9 volts but I am not sure so hopefully I'll be able to get the engine running again and then I'll run it for awhile and monitor the voltage.

    I also think the test of pulling the fuses and checking the current will be a good one.

    Thanks all, will post some new results soon.
    Tim
     
  10. timglen

    timglen New Member

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    Well, I have to thank everyone for the progress I made today, I think the main problem was the aux battery (although I am not 100% convinced yet). I put in the charged Optima and had some issues with lights on the dash but was able to resolve them (I hope it is permanent). The red triangle was there I believe because I had forgotten to reconnect a relay on the side of the drivers side junction box (no 90987-02027), not sure what it is for since they don't show it on the diagrams (just the 3 in the front). I cleared the other ones by putting a jumper btw pins 4 and 13 on the OBD connector and hitting the brake 8 times. The voltage of the aux battery stayed around 12.9 volts even after running it for about 5 minutes and when it was running it was between 13.7 and 13.8. The current was the same as it was in my last post but the meter did flash for a little bit when the Ready light went on and then came back showing 0 amps, is that correct?

    The interesting part of all of this is that I went to the toyota site /owners (I can't upload my comments where there is a url in it) and found out that it was taken to a dealer in May of last year. I called the dealer and they looked up the repair order number and told me that the car was towed there because it wouldn't start and they diagnosed the problem as an unknown fluid in the inverter and the recommendation was to replace the inverter. The owner decided against it and I assume that is when they donated it to the non profit organization where I bought it. That makes me a little nervous taking the Prius in for a techstream check since obviously the car will start. I would also like to get the brakes checked since I replaced the skid control ECU, is there a good site to find recommendations for garage's that work on Priuses? I live in Albuquerque, but have many friends in San Francisco, and so would like to take it to the Luscious garage there but not sure if it will make it that far (it has about 167,000 miles on it) and again not sure if it doesn't have an major problems. Like fluid in the inverter, does that mean I have to take off the lid of the inverter?

    Thanks again to all of you, without your help I would probably still be trying to find a short somewhere!
    Tim
     
  11. timglen

    timglen New Member

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    Last night everything looked good, the engine came on, there were no lights on the dash and the voltage showed 13.8 when the display showed the battery being charged, in addition no error codes showed up when I ran the techstream diag. Afterwards I disconnected the battery just in case, and it showed 12.9 volts.

    This morning (thinking I would be able to drive it) I put most of the things back together that I had taken off to do measurements of resistance, like the dash components, glove compartment, etc, reconnected the battery (the new Optima), and then tried to start it but without success.

    The Ready light won't come on, and I get these lights on the dash:
    ABS, Check engine, big red explanation point, tire pressure.

    the volt/amp measurements are these:

    off 12.7V
    push once 12.2V 6 amps
    push twice 12.2V 9.8 amps

    Techstream now shows C1241, U0073, U0123, U0124, U0126, U0293, B1650, B1660. Since C1241 means a low battery, does that mean that 12.2V is too low? And since this is a new battery does it mean that too much current is being drawn (i.e. a short somewhere)?

    The other thing that happens is if I press on the brake (after pushing the power button twice). I hear clicking in the engine compartment (inverter?), and the amps goes up to about 23 and the display goes dark and then comes back on. It shows P/S in red and sometimes the hybrid system warning light (sometimes it is off), see attached photo. Sometimes when I step on the brake I hear a fan go on in the engine compartment, maybe the same one that goes on when the engine starts, I am not sure but the amps go up to about 28. Also sometimes the gear display (P,R,N,D,,) flashes (see attached photo).

    It seems like Patrick was on to something when he mentioned and intermittent wiring harness issue. I wonder if the other reason might be the inverter with an "unknown fluid", could that be causing a short?

    When the problems are intermittent solving them becomes very complicated!

    Thanks again for your insight into these issues.

    Tim
     

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  12. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Remove all of the trim that you had reinstalled this morning. Try to get the car back to the condition it was in last night when it was actually working.
    2. Drive the car in that condition and see how well it runs and how long you can drive like that.
    3. If the car is stable with the trim removed, you can try measuring current flow when the car is in various states, but I do not think that is your problem.
    4. Move all visible wiring harnesses with the trim removed, and see if you can force the fault to come back. If you can then you will know the general area of the intermittent fault.
    5. DTC C1241 is reported by the skid control ECU. I think it is more likely that you have a fault in the wiring harness leading to the emergency brake power supply (the black rectangular box to the left of the 12V battery) or the wiring harness leading to the skid control ECU, than an actual 12V short. That fault is interrupting power to the skid control ECU, hence it thinks the battery voltage is low.
    6. Forget about the inverter for now, if you can measure 13.8V when the Prius is READY.
     
  13. timglen

    timglen New Member

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    Thanks Patrick for your suggestions. I disconnected everything and put it back to the state it was in when everything was working but now I can not get the Ready light to come on and the Red Triangle does not go away. I did some measurements of the voltages and ohms on the connectors on the skid control ecu based on the page I uploaded an image of and all the voltages were above 11 and all the ohms were below 1. I also checked the voltage on the connector to the brake control system and it was also above 11v (pin 5 to GND), I also attached a screen shot of that test.

    I played around with the wiring harness next to the skid control ecu but that didn't help. I keep rotating the 2 good batteries I have after charging them so the one in there now shows over 13v when nothing is connected. The more tests I do the lower it goes (especially if the engine fan goes on) so I don't want it to be a factor in my testing.

    I also ran health check again and got the same codes but this time C1242 showed up.

    Any ideas on what kinds of things I can try now? I am at a complete loss, especially since this is so intermittent.

    Thanks again,
    Tim
     

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  14. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Since you've measured voltages at the skid control ECU and the brake power supply and found them good, that would point to the skid control ECU being bad. However I think you've already replaced it.

    One possibility is that the ABS 1 or ABS 2 relays are intermittent. You could find the two relays, and hit them on the top with a screwdriver or other tool to see if you can encourage each relay to work. If that is the problem then of course you would replace the relays. They probably cost around $75 each at your local Toyota dealer's parts counter. The probability of the relays being at fault is low, if your voltage measurements do not show a problem.
     
  15. timglen

    timglen New Member

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    Yes I have 3 skid control ecu's the orignal and 2 I bought on ebay (I thought I destroyed the first one when I ran the CAN bus check with techstream, which caused the ABS and VSC lights to go on). I connected up the original SK ECU and got the same results.

    I hear clicking in the engine compartment when I press on the brake (w/o pushing the power button). I removed both of the ABS relays and the clicking noise stopped and then I inserted one at a time and found that they both click when I push on the brake. Is that normal? Maybe I should just replace them and see. Thanks for your tip because I did not know what the cause of the clicking noise was, now I do!

    I did try tapping on both of them with no results.

    Thanks again!
    Tim
     
  16. timglen

    timglen New Member

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    Thanks Patrick,

    I ordered 2 ABS relays on ebay (total $14) so will try them when they arrive. But something interesting happened yesterday. For some reason the radiator fan is going on when in IG-ON mode (this just started), and the current being drawn would jump up to 27 amps, I wanted to stop that while I am doing the testing with techstream so that the battery would last longer. I found out that the relay for the fan is in the Unit C box. One thing I noticed is that the Unit B box is upside down (see attached photo), and I don't know if the cables will allow be to reverse it. The other thing is when I disconnected one of the connectors in Unit C, the red triangle no longer came on in IG-ON mode and it reappeared when I reconnected it.

    Does this make sense? Does this give a clue as to why the red triangle is coming on?

    Getting an error when I try to upload the picture of Unit B, C. The label of Unit C is toward the driver's side while for Unit B it is toward the front bumper.

    Thanks,
    Tim
     
  17. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Turn off the cabin ventilation system prior to testing, especially defrost or any air conditioning function, as that may prevent the radiator fan from turning on. The high current drain is probably due mostly to the PTC electric heaters turning on while the radiator fan is a small contributor to the current drain.
    2. The orientation of the two integration relays B and C are correct as you have described them. The B label positioning is correct when upside down and nearest to the front bumper.
    3. Keep the 12V battery charged up with a battery charger or similar device.
     
  18. timglen

    timglen New Member

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    Thanks Patrick,

    I got the 2 ABS relays yesterday and I tried them out but no changes, but it was worth eliminating some possibilities since there seem to be so many. I tried using all of the buttons on the steering wheel to make sure no air was being sent to the cabin, and what I noticed was different icons lighting up on the dash (e.g. A/C) and I made sure that none of them were on but the radiator fan still comes on so I might be missing other possibilities since I have never used those features. Also I disconnected all of the connectors in Unit B and C and the radiator fan still comes on. The only exception is for the connector for the 2 15A fuses (IG2 relay, EFI M relay), when I disconnect that none of the dash lights come on. Don't understand how the fan can come on without the Fan No. 1 relay connected, unless there is something wrong with the wiring.

    I have been rotating batteries (charging them with the Optima charger) for quite some time, swapping them when the voltage gets below 12.4 volts so that I can be sure it is not a battery issue. Both of the batteries (one is Optima) are over 13 volts after charging.

    The behavior of the car now is something I have not seen before, when I go to IG-ON the lights on the dash go on and off 3 times before they stay on, during that time there is a clicking sound coming from the engine room.

    I believe I misstated which connector caused the red triangle light to stop going on, but now I just have to remove the 20A HEV fuse from Unit B to make it so the red triangle light does not come on. I will keep investigating this and let you know if I find out anything.

    This car is a real challenge since the behavior keeps changing but I really appreciate all the feedback!

    Tim
     
  19. valde3

    valde3 Senior Member

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    Only way to turn climate control system off is through MFD (touchscreen). Just turn the car to ACC (power button twice without brake) press climate button and then OFF on the screen. Then climate will stay off (probably until you disconnect 12V-battery).
     
  20. Patrick Wong

    Patrick Wong DIY Enthusiast

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    As you know, there are two fans sucking air through the radiator.

    The first, named "Radiator Fan", can receive 12V power from either the Fan #1 relay or the Fan #2 relay.

    The Fan #1 relay is activated via the engine ECU when that ECU thinks the engine coolant has gotten warm enough.

    The Fan #2 relay is activated by the AC amplifier when the AC compressor is running

    The second, named "AC Condenser Fan", receives 12V power from Fan #3 relay, also activated by the AC amplifier.

    The AC amplifier can make the two fans operate at either full speed or half speed via control of Fan #2 relay.

    Do you know what accident damage had been incurred by this car, prior to your purchase? Was the car hit from behind or in front?
     
    #20 Patrick Wong, Jan 31, 2016
    Last edited: Jan 31, 2016