Frequent Cycling Engine when AirCon is On

[treet007]

Hi there. I have a Gen I 2002 Prius with 125K miles. When the car is idling and the air conditioner is on, the engine turns off and on frequently, like every minute or so. So if I am at a stop light, the air con would be on (not on Max setting), and the engine would turn off, then on for a minute, then off for 30 seconds or so, then on again for another minute, etc. The car appears to function normally otherwise and I do not recall my car doing this before the accident. There are no pending codes when scanned.

One other thing is that I hear a hair dryer sound on the back if I am at idle and I turn off the air conditioner. It sounds like there is a fan in the hybrid battery compartment (in the back) and it is on. This occurs even if it is not over 80-deg F outside. I have heard this sound before (usually when it is super hot outside and I am idling per city driving), but not as frequently as I do now.

A little recent history on the car: it was in a major accident on Dec 31, 2008. The left side was hit, both passenger and driver doors at the pillar, but the hybrid battery area (and the engine compartment) were not impacted. The body shop (a regional chain who said they had experience working with hybrids and is I-Car "Gold" certified) had the car for over a month, and they apparently discharged the HV battery completely since I immediately got the code (P3006) and that they had to replace the 12V "cranking" battery in order to start the car. I told them they had to turn on the car for 30 minutes every week to ensure the HV battery was charged, otherwise a complete discharge can ruin the HV battery. Replaced the HV battery with a new one, but I did not replace the HV computer.

Is this normal and any suggestions? I was thinking of replacing the HV computer, obtained from the junk/recycling yard or eBay.

Thanks in advanced.

[Patrick Wong]

1. The engine will turn on whenever the air conditioner compressor has to run. Is it possible that your A/C system is low on refrigerant?

2. What is your method to determine there are "no pending codes"? A generic OBD-II code reader is not a reliable indicator since Prius has multiple ECUs that can generate DTC. You would have to have a Toyota dealer tech pull the DTC. However if you don't have any warning lights on, then chances are no DTC will be stored.

3. If your car really doesn't have any fault codes I don't see any point in replacing any ECUs. The traction battery does have a ventilation fan and it is not reassuring to hear it run if the ambient temp is not high. I can see why you would be concerned if you just had to spend $$$$ on a new traction battery.

4. It is not true that the car must run 30 minutes every two weeks for the sake of the traction battery which should be able to go at least a couple of months in storage. However this is true regarding keeping the 12V battery charged up if it was not disconnected.

[treet007]

Thanks for the responses. My replies are below (I did not repeat your statements above):
1. That is a possibility. I will have this checked, including the compressor itself.

2. My mechanic looked for DTC codes twice (at two separate times), and their were no stored or pending DTCs. He used the same reader when he pulled the P3006 code, indicating HV battery fault, and verified by two different Toyota dealers.
3. One thing I did not do is check the vent fan and the vents themselves. There is a cabin vent, and I should check the opening to see if there is any crap from the body shop. When I received the car from the body shop, it was so dirty from the dust that I had to vacuum the inside, including the ceiling.

4. This has been a considerable debate, but four notable sources indicate that a complete discharge of HV "traction" battery would cause faults:

A. From I-Car (the Inter-Industry Conference On Auto Collision Repair, is an international not-for-profit organization dedicated to training the collision industry):
* “Run the IC engine for 20–30 minutes or drive the vehicle to charge the batteries once every two weeks” [Topic C, for 2001-2003 Toyota Prius and Honda Insight]
* “Note: Extended storage times which result in the discharge of the low- or high-voltage batteries may result in the setting of DTCs and/or a no start condition.” [08EscapeHVModifiersGuide]

B. From Toyota: “(2) If you do not use the vehicle for a long time, the hybrid vehicle battery will discharge.” [Prius (2001-2003)-Things You Must Know (Hybrid Care)]

C. From Troy of Forest Hill MC (5/2/03): "I bought a new Toyota Prius March 15. I was shocked and alarmed to read on page 8: "If you do not use the vehicle for a long time (2 weeks or more), the hybrid vehicle battery and auxiliary battery will discharge and their condition is liable to decline. Therefore, in order to make up for discharging, charge them once in every two weeks for about 30 minutes by starting the hybrid system with all electrical components turned off." [www dot consumeraffairs dot com/automotive/toyota_prius_battery.html]
** This was the basis of my conservative approach in maintaining HV charge when the Prius is in storage. **

D. Independent hybrid research firm with NC State University: I am waiting for an official letter from this firm, but per my phone conversation, their research revealed similar HV battery discharge problems as noted above.

Now, I can only speak on the 2001-2003 Prius Gen I models. The 2004-2009 and the new 2010 may have improved HV system where such complete discharges would not occur like in the Gen I models, and hence you could store the vehicle for a longer period of time without recharging.Toyota FAQ on their corporate web site states, "For the hybrid vehicle battery, charge the battery at least once every two months by starting the hybrid system for about 30 minutes*. Check that the 'ready' light is on and all lights and electrical accessories are off. It is not necessary to drive the vehicle, but do not start the hybrid system in an enclosed area unless the tail pipe is connected to an exhaust hose to prevent harmful build up of fumes." So your statement is correct for the Gen II and probably for the Gen III, but not necessarily for the Gen I models. If you or others have contrary information for the Gen I, I would be interested.

[gippah]

Originally Posted by treet007

Hi there. I have a Gen I 2002 Prius with 125K miles. When the car is idling and the air conditioner is on, the engine turns off and on frequently, like every minute or so. So if I am at a stop light, the air con would be on (not on Max setting), and the engine would turn off, then on for a minute, then off for 30 seconds or so, then on again for another minute, etc. The car appears to function normally otherwise and I do not recall my car doing this before the accident. There are no pending codes when scanned.

This is the way this car normally functions when the AC is running on the Gen I Prius. Is this your first summer with it? I apologize for the other responses above from people who didn't know this and incorrectly confirmed that this is a problem.

As for the fan sound in the trunk, my fan back there was very noticeable in the weeks before the traction battery died. As this was last summer and I have a car that is one year older than yours, I'm hoping your battery isn't on the same schedule mine was. When driving the car on very hot days, accelerate slowly so you're not putting too much stress on that battery until the weather cools off and hopefully you can squeeze another year out of it.

[bwilson4web]

Originally Posted by treet007

. . .
4. This has been a considerable debate, but four notable sources indicate that a complete discharge of HV "traction" battery would cause faults. . . .

You may want to look at a datasheet for NiMH battery and study the chemistry. Wikipedia would be another good start as well as the RC hobby groups.

GOOD LUCK!
Bob Wilson

[treet007]

Just to let everyone know:
1. My mechanic found a "gap" in the AC compressor. This was causing the periodic AC problem. I will need to get a new AC compressor by this coming summer.

2. The AC clutch was initially replaced, and this did not completely resolve the symptom.

3. I can "reset" the AC when it blinks by turning it off, wait 5 seconds, and turning it back on. Hence the identification per #1 above.

Thanks everyone for your assistance.

[treet007]

Originally Posted by Patrick Wong

4. It is not true that the car must run 30 minutes every two weeks for the sake of the traction battery which should be able to go at least a couple of months in storage. However this is true regarding keeping the 12V battery charged up if it was not disconnected.

Patrick, check the attached document from I-CAR (page 2, second column). They recommend the 30 min/2 week recharge. For the Gen 1, someone else recommended 30 min/week recharge if it is in storage or not in use.