tbradford

It seems my 1994 LS400 is an ECM eater. It has eaten five. I need help in troubleshooting. The vehicle is in an independent shop and the mechanics are scratching their heads. Here are the symptoms:

The CEL light is off. The air bag light is on. The car will run well with a new ECM for a while and then will stall and in three days drain the battery. The ECM codes cannot be read consistently on a Snap-On 2500 or a Motus computer. In both cases the data stream flashes. As the ECM fails it has a hard time starting, transmission will not shift and rough or stalling engine above 2000 RPM. The mass air flow sensor and coolant temperature sensor has been replaced. I have a first world problem – I’m down to three cars! What should I do?

RA40

iTrader: (6)

You likely have a short that is causing this. About all you can do is tear into the car and depending on your resources, this one may not be worth it.

Raddison

The second you said "and in three days drain the battery" I thought short as well. Bust out the voltmeter and get comfortable checking voltages across fuses with the car off.

tbradford

Probably it would be sensible to salvage the car. However, the car does have some sentimental value; I inherited it from my dad last year. Is there a systematic way of tracing down a short?

Luxurexus

I read in another post this car was rear ended? I would start checking there.

BobN54

The first thing that comes to mind is a voltage stability issue. You may have an alternator with bad diode(s), voltage regulator, or a battery with a shorted cell. Have the battery load tested. If it checks out good, temporarily disconnect the alternator and run it on the battery only. Recharge the battery as needed with a battery charger. See if the problem goes away.

1GSLuVeR

Here is the wiring diagram if you need it:

http://www.lextreme.com/misc2.htm

RA40

iTrader: (6)

Start at the back and work forward. If as another has replied, check the area where the car was repaired for any wiring harness damage.

python

iTrader: (4)

first and foremost..do not take the vehicle back,find another shop that specializes in electrical
secondly...ask them how they concluded ur ecm was bad
thirdly....once the second ecm was determined to be bad..ask if they tried to figure out the cause and effect issue..meaning the ecm was the effect of another cause..so what is that cause?
fourth..ask for ur money back on any diagnosis and repairs, u wont get any money back for parts.
fifth..(if they refuse to give u any money)let them know if ur not reimbursed u will be calling BAR and will also give negative reviews on yelp and word of mouth can be just as detrimental.

FIVE ECM'S! are u kidding me..what a flippin joke!

tbradford

Sorry, for the sake of brevity and with the intent of narrowing the focus on the problem at hand, I failed explain that I paid for only two used ECMs. Also, the shop is charging only for parts (they call it a learning experience). Otherwise I would have abandoned the effort earlier. The shop really doesn't have the nack for troubleshooting. In the past I've had to get ideas from smart people in forums and relay that information to the mechanics. My HOA will not allow me to work on a car in my parking space.

tbradford

Let me add that when the car was rear-ended, it was pushed into the car in front of it, damaging back and front. The insurance company repaired it and everything worked fine for a couple of years after that. I like your suggestion and will pass it on. Thanks.

tbradford

Here is a picture of one of the failed ECM board.

Does anyone understand circuitry enough to suggest what circuit could have caused the damage (discolored board) at the capacitor?

python

iTrader: (4)

cap went out

RA40

iTrader: (6)

Wow...do the other ECM's fail at that same location?

Without a schematic for the tracings, that will be a pain to dig through. What is the underside of that like? Something is getting quite hot. That cap didn't burst unless it leaked from the bottom pin and caps can take some heat in their usual operation. Checking the pinouts of the connector tot the ECM for their specs is about all I could suggest.

Run that ECM by the parts or technician at Lexus or Toyota and see if they have any idea what may be happening.

GL

tbradford

Yes. There was one other ECM that I opened, and it had the same burned area at the same capacitor location. The other side of the board didn't look so bad. The area in question is in the vicinity of the scratch marks in this picture:

Not sure where I can find the pinouts and ECM specs - need to research.