Intermittent (!) Warning light, DTC C1300. What type of Skid Control ECU issue?

I think you can get access to the electrical connectors on that ECU (all the access you need for voltage measurements) with less work than that.

Here's it with the connectors unplugged. Looks like a lower finish panel was removed for this photo?

 

Hello Chapman I could not get the AC duct unhooked, Tried multiple times so suspected there was clip I could not get to. Cause I made it this step and there was white AC duct in the way and could not take it out, so have to see what I got wrong here. The troubleshooting instructions said u have to take measurements with wire harness hooked up, voltage and resistance. So have to see if I can grab the correct pins with very limited access. I have to try it next weekend cause my wife is still driving the car.

 

That photo came from a project write-up here by old-time member hobbit.

Maybe he'll have some details there, or might remember, how much work he needed to get there.

 

Read through his blog, it is fascinating / homebuilt gizmo. He did not take the ecu out, he did manage to take the AC duct out which I failed to get out. The main difference is he unhooked the wire from ECU and got the harness down to put his gizmo in. The DTC manual C1241/42 code requires to have the connector plugged into ECU. I will have to give it one more try to see if I can remove the air duct and be able to troubleshoot, hard part might be finding all the correct pins & wires. Attached instructions on getting the ECU out per toyota RM manual and getting the steering column is a bit of undertaking and hope to avoid it at all costs. I got to get the AC duct out to see if it gives me enough to troubleshoot.

I got the file & image from a different post.

 

Hello Chapman, I got a big question. On troubleshooting steps for power supply, instructions said to measure Between B18 connector pin 5 to ground with connector plugged in. It did not tell me if the car is supposed to be On, On (Ready) or Off. There was nothing with car off, so I turned it ON (No ready) and measured and it was 11.73V. So moved to next step of Check harness and connector (still struggling with getting access and can not find any videos online with my search terms) but I am link should the car be in which state. Any insight.

 

The C1242 code is for one of the two IG power feeds is missing (IG1 vs IG2). These are switched IGnition feeds, so the car should be ON or Ready.

Toyota is pretty bad about not giving details about what is needed to actually set any given code. So I don't know how much of a voltage difference between IG1 to IG2 has to exist, or for how long (1sec, 0.5sec, 0.1sec?). Sometimes I have to use a scope to view what's going on with a circuit.

There could be a wiring problem for the power feeds. Could be a bad connection (corrosion or loose terminal fit). Could be a problem on the ground side. Could be a bad brake ecu.

Posted via the PriusChat mobile app.

 

Well, the repair manual says for C1242 INF 87 "Voltage is applied to IG2 terminal, but not applied to IG1 terminal for at least 4 sec." and INF 88 is the same but for swapping IG1 and IG2.

So ok, it doesn't say exactly what difference in voltage trips it, but I think typically when I've seen freeze frames of a C1242 posted here, one voltage will be 11 or 12ish and the other one will be zero, or, like, 4½ or something, so the Potter Stewart rule turns out to be good enough.

 

In order to keep the repair manual readable and also to keep it from getting bloated, it assumes the technician has completed various prerequisite modules at "Toyota University" so much of the detailed information that they expect a technician to already know is not included. Further, with the right training, some details fall in the obvious category so again not included. In some cases, the technician should be able to work some things out for themselves which you demonstrated above when you said, "one of the two IG power feeds is missing (IG1 vs IG2). These are switched IGnition feeds, so the car should be ON or Ready."

All in all, for home mechanics like us it makes it more challenging to work through some of the steps when all you have is the repair manual and this knowledge gap.

 

It doesn't help if "someone" (cough) skims over the diagnostic procedure without really READING it. In this case there is enough info present about the code setting criteria that one should be able to figure out the problem.

In "other"cases , the engineers decided that they will only give "replace this part" codes, which USUALLY is understandable. There are several assemblies that were not designed to be serviced except by replacement.

It is just that not every real-world fault fits neatly into the engineer's pre-planned view.

Posted via the PriusChat mobile app.

 

All, finally after some brute force led by frustration I took the AC duct out that was preventing access to skid control unit, I guess I was being too gentle with it. All the buttons that I had to unplug to get myself some room I plugged back in so they would not corrupt in any way my findings. Use a FLUKE 101 multimeter.

1. Battery voltage (Range 10 to 14v): 12.85V Car ON Ready, 12.73V Car off.
2. Brake Control pwr supply (Range 10 to 14V) (B18-5, Black wire) ( some ins/outs went through the front driver door switch so decided to check its influence) - PASS
   1. 11.93V Door Open CarOn NoReady
   2. 11.87V Door Closed CarOn NoReady.
3. Check harness & connector (Range 10 to 14V) (tested carr-off & Car on NoReady) (Manual did not say on where the car needs to be on or off)
   1. CarON No-Ready
      1. S8-7, IG1,12.07V
      2. S10-5, IG2, 11.73V
      3. S8-3, +BI1 11.85V
      4. S9-5, +BI2, 11.85V
   2. CarOFF
      1. S8-7 0V
      2. S10-5 0V
      3. S8-3 12.6V
      4. S9-5 12.6V
4. Check wire harness (Range < 1ohm) Tested with car-off as it is for continuity. Pass if below 1ohm
   1. S7-1, GND1, 0ohm
   2. S8-1, GND2, 0ohm
   3. S8-2, GND2, 0ohm
   4. S9-1, GND5, 0.1ohm
   5. S9-2, GND4, 0ohm
   6. S10-4, GND6, 0ohm
5. Inspect skid control unit terminal voltage, CarOn Ready state.
   1. S7-2, R1+, Range 8 to 13V, measured 13.50 (did it twice after a time gap of 30min to confirm, within +/- of 0.1V from 13.5)
   2. S10-17, R2+, Range 8 to 13V, measured 13.39 (did it twice after a time gap of 30min to confirm, within +/- of 0.1V from 13.39)
      
   3. S7-12, SR1, Below 1.5V, measured 0.086V
   4. S10-15, SR2, Below 1.5V, measured .084V
   5. S7-3, BS1, Range 10 to 14V, measured 13.5V
   6. S10-7, BS2, Range 10 to 14V, measured 13.6V
6. I restet DTC after this. My wife reported to be that they lights are on again, so this evening will see if they are same DTC that came up.

Per instructions of C1241 dignostic manual Skid control unit failed case of R1+, R2+ not with in range. But C1241 error and the subcode I got was 83 which says trouble area is Brake control power supply or its assy, and Hyrbrid control system. No error from techstream from Hybring control system. I do need a new brake actuator cause of C1256 & C1391.

So refreshing my code list. C1241 FFD subcode 83, C1242 no ffd, C1256, C1300, & C1391. Now funny or confusing thing is the IG1 & IG2 terminal voltage from C1241 ffd data are rported as 6 to 8.5v for both but not the measurements I took. I guess it depends on where it is measuring internally.

 

Purchased both Skid Control Unit - USED, and brake actuator - NEW ($1179 ). Hope it drives long enough to get what I put in it to fix it. Almost thought of junking it but looking at new car prices I am taking the chance of fixing it. I had a 2004 prius with 330K miles on it with no issues (other than stuff wearing out) and this one is other way around.

 

I am back here, can not seem to find the abs actuator (new) 44500-47141. Contacted 3 Toyota dealers no one has stock and olathe website says stock but they cancelled my order as they don't know when the part is going to actually come in as Toyota does not have it. Anywhere else I could look.

 

Everything is in, ECU used & new ABS actuator. I could not fish the actuator out with out taking the brake tubes out of the car like some videos, but installation went well, as always, never repaired a car where I did not encounter a rusty bolt that breaks. All in all actuator is bled, zero point calibration done. Drove in the street, this weekend is more stress test, went through more than 32oz of fluid to bleed. I have to say brake bleed I felt was most complicated. Line wrench definitely takes stress out of handling brake line connections and magnetic sockets would have helped as well but I managed with out them but took time. No codes on dash from few minutes of driving I did last night, will report from this weekends driving.

Thanks for everyone who has helped answer some of my questions along the way.

Techstream is a clunky tool but it got the job done for me.

 

No codes to report yet. Brakes are working fine, HV system working better now as it is able to take better load. I have not done any heavy braking like slamming the brakes, to check for any pull to a direction or if ABS is working okay. Only hitting 40mpg so need to figure out why I am not getting 44mpg like before but could be a separate issue.