1995 SC trouble codes and diagnostic

I hooked my 95 up to a very good scan tool last night. It had a BUNCH of code history, but 2 active codes. Here's the 2 active codes:

Po134
P1361

When doing the active scan it reported 1 error on the camshaft sensor. o2 voltage wasn't swinging even though the car was warmed up, it was just sitting at .45 volts.

The history codes are:

po101
po131
po134
po171
po341
po342
po640

The car gets awful gas mileage and from time to time will stutter going down the road (light miss).

Also I have an A arm bushing that needs replaced, BUT aside from the codes and the bushing this car's running great ") Really came a long way since I rescued it from a life of rotting out in someones yard!

P0134 Heated Oxygen Sensor Open Circuit.
This code is why you're seeing .45v for the O2. There is an open in the Low Reference (tan wire), or the Signal Circuit (purple wire). Either the O2 is bad, or you have a wiring problem. More than likely, it's the sensor. This fault will also cause your gas mileage to be shit, and the car may run stupid. P0131 is also an O2 code (voltage low).

P1361 IC Circuit
This code will set if the PCM reads an open in the IC circuit, or an open or grounded Bypass circuit during startup. This code will also cause your gas mileage to be bad, because this particular fault deals with timing directly. The initial engine timing (during startup) is controlled by the Ignition Control Module. After the car starts, the PCM applies 5v to the IC via the Bypass wire. This "turns off" IC timing and the PCM takes over. Either the ICM is bad, or you have a wiring problem. In extreme cases, I've seen the PCM cause this code, but it's extremely rare.

P0341 and P0342 are both Camshaft Sensor codes.

P0101 MAF Sensor Circuit

P0171 Fuel Trim Lean.
This code can be set as a result of P0134 (O2 code)

P1640 Quad Driver Module No. 1 Circuit
This code is related to the Boost Bypass Solenoid, The EVAP Purge Valve, and the TCC Solenoid. I'd worry about everything else before you tackle this one.....


Either you have a few different problems, or 1 or 2 problems causing multiple codes. Where we gonna start?

So my plan of attack right now is to pull and clean the ICM (I hear they have corrosion problems that prevents them from grounding sometimes) and replace the heated o2 sensor. I'm really hoping the rest of the issues are related to me working on the car a while back (cleaned the MAF out, cleaned some sensors etc.).

Should I be looking into a camshaft sensor as well? I know it's giving me some codes but could I have caused this by messing with it before?

I may be inclined to think that the ICM is throwing false Cam Sensor codes. I would clean what you're going to clean and see if it helps before we go chasing the Cam Sensor. Also, check the plug that goes into the ICM for any corrosion or broken wires. It's quite common that that harness breaks a wire (it's a GM 3800 thing). Specifically, you want to check the Tan w/Black stripe wire, and the White wire on that harness. Those are the IC Bypass and the Ignition Control circuits that are responsible for P1361.

Yes absolutely replace that O2.

If you were unplugging and messing with things before, the only way you would have codes stored in history is because you had the key in the RUN position when you unplugged them. Codes will not be stored if the key is never turned on.....

Ran the car with the MAF off and some sensors unplugged so I'm pretty sure that's where a few of the history codes came from. By "break a wire" do you mean along the actual wire, or the harness gets a bad connector?

I just ordered a new NTK o2 sensor. I can get a generic ICM for around 30 bucks (local auto parts stores carry VERY generic parts and they cost 5 times that LOL) I'm going to check the wiring and such first.

brian10962001 wrote:

Ran the car with the MAF off and some sensors unplugged so I'm pretty sure that's where a few of the history codes came from. By "break a wire" do you mean along the actual wire, or the harness gets a bad connector? I just ordered a new NTK o2 sensor. I can get a generic ICM for around 30 bucks (local auto parts stores carry VERY generic parts and they cost 5 times that LOL) I'm going to check the wiring and such first.

I literally mean that the wires going to the ICM "snap", or the insulation gets rubbed through and the copper turns green (corrosion). It's a really easy visual check for the most part. You want to check from the connector itself to about 8 inches down the harness. If they all look ok, and the tape and/or conduit is in good shape, I wouldn't bother to go any farther than a visual inspection of it.

I got a chance to look over the wiring in my car yesterday, it looks pristine. All of the loom is intact (be it a bit brittle) and I see no spots that are melted. The Camshaft sensor FEELS dry as if it's never had any oil, or coolant splashed over it, it had an aged layer of dusty grime but that's it. I'm conflicted now, and a bit short on funds. I'm thinking of changing the ICM first, but I'm a bit confused as to the function of code p1361. I'm assuming it's to blame and not a dead camshaft sensor, but it looks like the car could set this code if it never got the reference from the cam sensor. I should have the o2 sensor today and if it's not rainy I'll swap it in so at least I feel like I'm making some headway here. I really don't want to pour money into a cam/crank sensor and icm only to find out I need a pcm but I'm afraid that's where this is headed.

As for P1361 and P1640....there are some members on here that have dealt with that code(s) before. Hopefully someone else can chime in and help you with that concern. I've posted the schematics for that code before, you can find it HERE if it will help you.

Me, personally, haven't had the "pleasure" of dealing with these codes on my car, but I've had to deal with them on Bonnevilles and what-not. I just follow the flow charts and eliminate things one-by-one. Unfortunately, these codes aren't as easy as "oh shit, the sensor went bad", as there are quite a few contributors that can set them.

As to the p1640 code there is a write up with VERY detailed instructions from Nigelf in the series one tuning section. The most common cause for that code seems to be the boost control solenoid which while difficult to find should only cost around $40 plus whatever it takes to ship. A bad bcs will cost you heavily in gas mileage and depending on where the valve actually stopped moving could cause low rpm kr if its building mild boost down low where its not supposed to. Sorry can't help much with the other code as I've never expirienced it. Hope that helps and good luck!

P1640 is a history code, It was also WAY down on the list, so it had been a while since it happened. I'm hitting the junk yard today looking for an ignition module and cam sensor (should be cheap) along with a fender trim. I'm really leaning towards the problem being the computer but I'm going to go with the cheap stuff that I can pull from the yard first. Apparently when the SSEi Bonnevilles start throwing these codes it's usually the wiring or the computer. I would just take my ignition module to Auto Zone to be tested, but my luck it would pass every test, but fail again when it was re installed!

brian10962001 wrote:

P1640 is a history code, It was also WAY down on the list, so it had been a while since it happened. I'm hitting the junk yard today looking for an ignition module and cam sensor (should be cheap) along with a fender trim. I'm really leaning towards the problem being the computer but I'm going to go with the cheap stuff that I can pull from the yard first. Apparently when the SSEi Bonnevilles start throwing these codes it's usually the wiring or the computer. I would just take my ignition module to Auto Zone to be tested, but my luck it would pass every test, but fail again when it was re installed!

For the ICM, did you consider getting a small tube of conductive heat sink grease, like $3.00 only, at Radio Shack or a tube of NoAlOx from a Home Depot or Lowes (similar pricing). When you reinstall the ICM use the grease in a dollop in the middle of the (cleaned) aluminum panel, it will spread and push the air out preventing corrosion and pushing any residues out the edges where of course you then wipe them off (!). And do you think you should take care to avoid bent pins on the connectors? Also - if you have/get a multimeter ($12 to $30 at walmart or radioshack or such) measure all the coil secondaries they should be around 7000 ohms. If not then check between primaries and secondaries for shorts. Be sure to clean and lube (heat sink grease) the contact surfaces before reinstalling each coil.

Finally, what do you think about clearing the old codes as you progress in the work?

HTH

Albertj

ICM will be cleaned and thermal compound treated before being put back on. I really don't think the coils are bad, the car runs good 99% of the time. I think when it slightly misses it's because the SFI is off considering it has no reference.

All codes have been cleared so far, I have no access to the scan tool to do this, a friend of mine works at a garage and borrows the big scan tool when I need it. It's good to have friends with access to things like this, that machine is pretty amazing!

brian10962001 wrote:

ICM will be cleaned and thermal compound treated before being put back on. I really don't think the coils are bad, the car runs good 99% of the time. I think when it slightly misses it's because the SFI is off considering it has no reference.

All codes have been cleared so far, I have no access to the scan tool to do this, a friend of mine works at a garage and borrows the big scan tool when I need it. It's good to have friends with access to things like this, that machine is pretty amazing!

yes it is good to have access to the scan tools; hopefully you can get your own before too long passes. Good luck with everything and keep us all posted!

Ok i hit the big junk yard pull a part today, first car i laid eyes on was a green Riviera. I pulled the ecm and it was a 96 "(. I then found 2 94 Lesabres and grabbed the ecm's. Interestingly both are remans! I noticed that there were virtually no icms to be found! So apparently icms and ecs are problematic in these! o2 sensor and ecm will be swapped in along with cleaning the module on Sunday. Ill keep you posted.

brian10962001 wrote:

Ok i hit the big junk yard pull a part today, first car i laid eyes on was a rivn pulled the ecm and it was a 96 "(. Found 2 94 Lesabres and grabbed the ecm's. Interestingly both are remans! I noticed that there were virtually no icms to be found! So apparently icms and ecs are problematic in these! o2 sensor and ecm will be swapped in along with cleaning the module on Sunday! Ill keep you posted.

No the ICMs are not problematic so much as they are prone to fry if they are mis-installed. You have to be conscientious about the R&R or they will fry themselves.

Why none to be found? Because they are interchangeable on the 3.4 and 3.8 and 3800 SC engines from around 1991 on, on most GM cars, and can be easily removed and sold. For instance one way the extended warranty people make money is by insisting on using used parts in car repairs. People take their car to the marque's dealer thinking they are getting factory parts in their repairs and that's just not the case due to the constraints of the warranty companies.

Albertj

Well warm weather finally arrived to stay! I spent a day taking off the ICM, cleaning all coroion from under it, and swapping out the o2 sensor. The sensor in there was a Bosch sensor with the brown wire grounded to the case, someone had broken that wire. It was VERY easy to remove, because it wasn't tight enough!

The car always had a tick when it started up, looks like it was the o2 sensor being a bit loose. On the ICM, I pulled it off, cleaned the mouting pad, cleaned the ICM itself and coated the bottom in white heat sink grease. The ICM looks to be a generic parts store item as it only had a p/n.

When all was said and done, the check engine light is still on, and the car is still down on power, BUT I'm not to concerned about it because I feel the culprit is the PCM. I still have yet to swap that over, I wanted to go through a process of elimination first. If I get time this week I'll swap over the PCM and see how it acts.

brian10962001 wrote:

Well warm weather finally arrived to stay! I spent a day taking off the ICM, cleaning all coroion from under it, and swapping out the o2 sensor. The sensor in there was a Bosch sensor with the brown wire grounded to the case, someone had broken that wire. It was VERY easy to remove, because it wasn't tight enough!

The car always had a tick when it started up, looks like it was the o2 sensor being a bit loose. On the ICM, I pulled it off, cleaned the mouting pad, cleaned the ICM itself and coated the bottom in white heat sink grease. The ICM looks to be a generic parts store item as it only had a p/n.

When all was said and done, the check engine light is still on, and the car is still down on power, BUT I'm not to concerned about it because I feel the culprit is the PCM. I still have yet to swap that over, I wanted to go through a process of elimination first. If I get time this week I'll swap over the PCM and see how it acts.

In many cases the CEL will stay on until you use a scan tool and reset it. Probly want to find out what that code is; could fix one thing and uncover another. Eventually you'll get it straightened out.

I've had that cel go off before, I thought on OBD2, it was 3 ignition cycles with no code and you were back to no CEL? OBD 1.5 I thougth was gone as soon as the condition was removed. It's a pain getting that cel reset I'll try the PCM this weekend and if it stays on I'll have to call my friend to borrow the scan tool again.

Maybe I'm wrong on this but I thought that if you disconnected the battery for about 30 mins it would clear all trouble codes from the memory without needing to use a scan tool. If that is true didn't you have to disconnect the batt to change the icm? If so and the cel is still on then you probably still have an active code that is re triggering it. If possible I'd check codes again before changing out anything else. I guess its also possible that you changed one bad icm for another bad icm to get the same code again, but without pulling codes its all guess work. Having a friend with a scan tool is great, but having your own is even better. When you're ready to buy one there is a post about which ones work best for the 95s

Derek wrote:

Maybe I'm wrong on this but I thought that if you disconnected the battery for about 30 mins it would clear all trouble codes from the memory without needing to use a scan tool. If that is true didn't you have to disconnect the batt to change the icm? If so and the cel is still on then you probably still have an active code that is re triggering it. If possible I'd check codes again before changing out anything else. I guess its also possible that you changed one bad icm for another bad icm to get the same code again, but without pulling codes its all guess work. Having a friend with a scan tool is great, but having your own is even better. When you're ready to buy one there is a post about which ones work best for the 95s

It is correct that if you disconnect the battery long enough the CEL will go off.

It is correct that many codes reset after a few run cycles if they do not recur. They can stay in "memory" though.

I'm not a big fan of spending money but if you have a car this age one of your issues will be that there's not that many people around who even really know how to maintain them right so if you're going to use it as a daily driver you're maney ahead getting your own scan tool. You can use the search function on this site to find good info about your choices. The 1995 is OBD-I with an OBD-II connection.

OK big update. I changed out the PCM and the TRACTION CONTROL and SERVICE ENGINE lights went out when I started the car. The car has picked up a serious amount of top end power and I can actually hear the supercharger working now! I'm not out of the woods yet though, after 45 minutes or so of driving the SES light illuminated. It goes off whenever I restart the car so it's something intermittant. I will be hooking it back up to the code scanner soon and driving it around so I can get a full diagnostic on it. Oddly enough the gas mileage is still pretty dismal. I averaged 21mpg all highway/interstate, up from roughly 18-19. At least it's moving in the right direction

brian10962001 wrote:

OK big update. I changed out the PCM and the TRACTION CONTROL and SERVICE ENGINE lights went out when I started the car. The car has picked up a serious amount of top end power and I can actually hear the supercharger working now! I'm not out of the woods yet though, after 45 minutes or so of driving the SES light illuminated. It goes off whenever I restart the car so it's something intermittant. I will be hooking it back up to the code scanner soon and driving it around so I can get a full diagnostic on it. Oddly enough the gas mileage is still pretty dismal. I averaged 21mpg all highway/interstate, up from roughly 18-19. At least it's moving in the right direction

You need to pull the stored codes. The car will store many of the intermittents so you can diagnose.

You sure could use a scan tool. I do not have one for you. If you search on this site thoug you will find recommendations, and if you search on eBay you should find used ones (for the 95) for short money.

Albertj

I replied to this the other day but I guess it didn't post. I ended up getting an OBD2 to USB program off of eBay for 16 bucks that supposedly does all OBD2 codes. I know it's a gamble if it will work for the Riv, but I was getting it for my girlfriends car so we'll find out. A friend of mine works at a garage and they have an up to date GM Tech 2. I have him bring that out whenever I need to scan it.

The girlfriend has been driving the Buick every day and on the last tank it got 22.5mpg! I'm hoping it's just taking drive cycles to get the prom mapped out. The car hasn't stumbled a single time since I did the work on it, and I'm still surprised by the power! It has more top end pull than my dads Riv with lower miles.

I'll post up if the code scanner works, and what codes I get from it whenever I get them pulled.

Ok I just had codes read on my 95 riveria it had 3 in the computer 1 p1630 2 p0341 and p 0705 can anybody make any sence of these and what do they mean thanks for your hepl

Here is what I found:
P0341- Camshaft Position Sensor A Circuit Range/Performance (Bank 1 or Single Sensor)

P0705- Transmission Range Sensor/Switch Circuit Malfunction (PRNDL Input)

P1630 - System Voltage High or low

Id probably start by checking battery voltage running, if you havent already