1996 STS Engine cuts out when coming to a stop

[WalRob1]

Sometimes, when my foot is off the throttle and the engine revs get low (say under 1,000), the engine cuts out. The first time this happened it happened frequently over a couple of days then the problem disappeared for a month or so. Now it has returned and is more frequent.

This occurs primarily as I come to a turning. Hence I'm using the brakes, foot off the throttle. If I can keep my foot on the throttle, I can sometimes avoid the engine cutting. But this is dodgy driving behaviour.

The fault is however, intermmittent. It has occured once or twice when I've been cruising towards an exit ramp about to leave the motorway. Most of the time, it's at very low speed, on local roads, just before turning.

If I sit in my driveway with the engine idling, the revs may fluctuate and the engine may cut out - but not always.

Engineers I've spoken to have suggested the Throttle Position Sensor (TPS) is failing or that the Exhaust Gas Recirculation (EGR) valve may be sticking/broken. But nobody seems certain. The approach seems to be, "Could be X, let's replace that and see.", piece by piece.

So far,I've spent over $800 trying to get this fixed, including needing to get the computer (ECM) replaced when an engineer tried to update it.

With the replacement of the EGR quoted at over $400, I would really like a better sense of what is wrong.

About 80 miles after replacing the computer, current dashboard displayed trouble codes are: PC1571, RS0038, PZ2042. Historic codes are myriad.

Any help or advice you guys can give me will be gratefully received.

[Cadillac Jim]

The first thing to do is to read the OBD trouble codes and see what the car's computers have detected as problems. The only CURRENT code that you cite that is on my list is

P1571 Traction Control Torque Request Circuit

This is a signal from the EBTCM to the PCM and is not likely causing your problem. The other two, probably a C0038 thrown by the RSS module and B2042 thrown by the PZM, I don't have in my list. A quick web search on those codes shows them to be related to the TCS and power mirrors.

I suggest that you reset the PCM codes, drive the car, then check the codes again before you turn off the key. This will keep problems just detected as CURRENT. Turning off the key throws everything to HISTORY. Post the persistent codes here, including HISTORY codes, and we can help you find the problem.

One thing that does bother me is the CURRENT P1571 means that you have an ongoing problem with the wiring between the PCM and the EBTCM. Perhaps you could begin by going over the connectors to the PCM and the EBTCM and make sure that both connectors are clean, tight, and in good shape. Make sure that none of the wires will pull out of the connector easily, and that none of the terminals are pushed into the connectors. The EBTCM connector has a snap clasp, and a holder that clamps over it to keep it tight; make sure that those parts are not missing.

[WalRob1]

Thank you very much for your kind assistance Cadillac Jim.

My apologies for my tardiness - I have been traveling and did not have my login info.

State of play:

I ended up, with great trepidation, awfully carefully replacing the EGR myself. Since then, the engine has run smoothly (very occasional knocking), the MPG appears to be up by about 5MPG. There are no engine hesitation or stalling problems. Total cost about $50 instead of the $400 quoted!

I just had it reinspected and it has failed on license plate lights only. So I'm roadworthy, once I've figured out how to access and change the bulbs.

However, I'd love to sort out any remaining significant issues.

Jim, the current full list of codes from the dashboard display.

Note: With the ignition on but the engine not running (suffix H=history, C=Current):

PC1139C PC1381C PC1571C RS0038C PZ2042C

PC0174H PC0300H PC0603H PC1380H PC1602H PC1644H IP1552H NO ACM CODES NO SDM CODES NO TCS DATA PZ1558H IR1470H NO RFA CODES NO CCP CODES

Does this modify your recommendations on how to proceed?

Thanks again Wal

[Cadillac Jim]

Current
P1139 Heated Oxygen Sensor (HO2S) Insuff. Switching Bank 1 Sensor 2
P1381 Misfire Detected - No Communication with Brake Control Module
P1571 Traction Control Torque Request Circuit
B0038 AUX switch open/shorted to battery

NO TCS DATA

PZ2042C ?

History
P0174 Fuel Trim System Lean Bank 2
P0300 Engine Misfire Detected
P0603 Control Module Long Term Memory Reset
P1380 Misfire Detected - Rough Road Data Not Available
P1602 Loss Of EBTCM Serial Data
P1644 Traction Control Delivered Torque Output Circuit
B1558 BCM EPROM Checksum Error
IR1470H ?

I would start with the CURRENT codes. The P1139 means that either the heating circuit or the oxygen sensor itself is bad on the front of the cat.

The B0038 is an air bag error code. It appears to be the passenger side air bag. This code can be thrown by a short or a bad ground. It may be that someone tried to disconnect the passenger side air bag. Be VERY careful working with air bags because they are basically controlled explosive devices. A lot of people have been hurt by air bags going off at the wrong time.

The P1571, P1380, P1602, P1644, and NOT TCS DATA all tell us that the EBTCM is offline. The CURRENT P1571 tells us that is just down, that the requested torque signal to the PCM that the EBTCM uses to tell the engine to back off is not valid.

The rest can wait. I would check the oxygen sensor wiring to the one on the front of the cat and if it is good I would replace that oxygen sensor. You can check the wiring on the air bag. I would disconnect the battery ground cable before I messed with the air bag wiring.

It's pretty clear that your EBTCM is inoperative. I would start with looking at the three fuses that I mentioned. If the stop lights work, you can focus on the 50 Amp BRAKE MaxiFuse and the 10 Amp ABS fuse in the underhood fuse block. Then, the EBTCM connector is the next place to look. Make sure that the ground on the back of the ABS motor is good, and that the resistance on the black wire in the EBTCM connector to ground is well under 1 Ohm. Check the big red wires on the EBTCM connector; both should always have 12 Volts on them even with the key off. With the key on, the big pink wire should have 12 Volts. If all that is OK and you are still getting a P1571 CURRENT, you need to start thinking about getting the EBTCM fixed.

[WalRob1]

Jim,

Is it reasonably easy to get to the O2 sensor in question and to replace it?

Are there any diagrams or instructions you are aware of that I can review before commencing doing this?

I have not been able to check the wiring you suggested. Is the EBTCM under the air filter?

BTW, I checked the fuses, "50 Amp BRAKE MaxiFuse and the 10 Amp ABS fuse", which both do not look burned out. What was the third fuse?

Thanks again wal

[Cadillac Jim]

There is a 20 Amp BRAKE fuse that powers the stop lights. If the stop lights work, you don't need to look for it.

Bank 1 Sensor 2 is the front oxygen sensor on the cat. It's easy to get to from under the car. Getting oxygen sensors out is tricky. The FSM says that the car should be 120 F or warmer so it doesn't stick in the threads. I suggest a propane torch to warm it up.

The EBTCM is under the air cleaner. It's quite low. Some people prefer to access it from under the car. You need to remove the air cleaner to get at it from the top (and it's a reach), but you need to remove the splash shields to get at it from the bottom.

If you want diagrams, you need a FSM. I suggest you get one from eBay. It's two volumes. If you want a specific diagram, someone can scan it in for you. I have a 1997 FSM which should apply to the 1996 model year with very few differences.

[barczy01]

Have you taken a fuel pressure test, Have you replaced the pump recently? Check your ignition coil tower and make sure they are nice and clean. When it does stall, does it chuggle and stall or is it what i call a quick phantom stall?

On replacing the left radiator side o2 sensor, get it from underneath. Remove the black shield with 3 10mm ten screws and put a 7/8 wrench on it. Don't use a bosch sensor.

[Cadillac Jim]

What's the problem with Bosch HO2 sensors? I just put one on my wife's 1999 Grand Am.

[barczy01]

I am not a big fan of them. I have had problems with them out of the box and within a months time. I even had an issue with one on my chevy pickup after a week. I stick with the ac delco ones for GM and have not had any issues.

[Texas Jim]

What's the problem with Bosch HO2 sensors? I just put one on my wife's 1999 Grand Am.

On the other DTS board, a few people used Bosch instead of AC Delco and had to replace them again before long.