Hi,

Lots of good advice on this forum, so I'm hoping someone can help me with some problems I'm having with my 1994 Volvo 850 GLT's ODB 1 unit. I've had this car about a month and it seems in really good condition and good working order except for these two issues, which I didn't pick up during my inspection.

The main problem I have is that there is some surging and near stalling, mainly when I don't have my foot on the accelerator, i.e. when idling, braking or making slow sharp turns. This only happens once every ten minutes or so, and the engine runs well the rest of the time (except for a little blow by). Sometimes the revs blip about 500 RPM, as if someone is pressing the gas pedal. Sometimes the revs fall sharply down to about 400 RPM and it seems like an automatic choke happens to stop the car from stalling. It has stalled twice now in the 400 km I have driven it. I looked through some other forum posts and the popular solutions seem to point to an IAC valve issue or a generally gunked up throttle body. I am waiting for a new IAC valve to come in, so I'll see whether changing that part and cleaning the throttle body will solve that problem in a week or two.

When trying to diagnose this problem, I tried to use the car's ODB 1 to get some engine codes. My understanding is that you can just plug the cable on the ODB casing into the ODB port, push the black the button and wait for the lights. I also understand this should be done without the key in the ignition. Anyway, I'm not seeing any lights. I also notice that I don't see the CEL when the key is in the ignition and the motor is off. I am seeing the service light on now, but I don't know whether there is any dependency between the service light, the CEL and the ODB.

In Australia, you need to get a roadworthy certificate to transfer registration of a car. I believe you can't get a RWC if the CEL is on. The owner said they had to reset the engine computer a couple of times to try and clear the light, but now I suspect they may have just unhooked the CEL or ODB. Anyone know how I can start going about reconnecting or testing my ODB unit? I had a look for other postsd about this, but couldn't find anything.

Cheers,
Dan

 

Actually, the ignition has to be turned on to use the OBD port. It's the same as OBDII. Turn the key to the on position, position II, then try to pull the codes.

 

Also check the fuses, I'm not sure which one it is but on the fuse box lid it says "diagnostics".


Yes the ignition needs to be on, but the engine not running, and you want to put the probe into socket A2 to read codes from the CEL

 

A third point is that the "service" light is simply a calendar. It knows nothing and means nothing. It just lights up 5000 miles after it was turned off (don't quote me on the number of miles there...)

 

Ok, so with the ignition in position 2, I have LEDs now on the ODB. I'll wait for some daylight and then see what codes I can grab. Thanks for all your help.

 

The CEL bulb is likely blown out.

 

 

Rspi, YouTube is down for the count. I wouldn't even bother with posting links or embedding. It just won't work. Actually, since that's the case, here's the next best resource to have. http://www.matthewsvolvosite.com/read-codes-volvo-850

 

OK, so I'm back with some codes. The so-called problems with the ODB was just my mistake. Here are the codes:

A1
2-3-2: Vehicle speed sensor signal absent
1-1-4: Break in driving mode selector circuit

A2
1-2-1: MAF sensor signal absent or faulty
1-2-3: Coolant temperature sensor signal absent or faulty

A6
3-2-4: Camshaft Position sensor (CMP) signal missing sporadically
3-1-4: Camshaft Position sensor (CMP) signal missing or faulty

A7
1-2-2: Temp. sensor interval too long

I still have my original problem, i.e. revs dropping or surging and occasional stalling. A bit of further investigating shows I have a small oil leak above where the CMP is and I suspect this is leaking into the CMP, especially since someone has applied some sealer around the CMP.

Would oil leaking into the CMP sound like something that could cause this problem? The problem is really intermittent; the car will drive great for as long as an hour, then go through a bad patch and then start driving well again leading me to think oil is making its way into into the unit then back out. The problem seems worse after highway driving so maybe the higher engine pressure is forcing more oil out of the damaged seal and increasing the likelihood of oil entering the CMP.

I'm clearly no mechanic, so I guess I'm just asking someone to say whether that this sounds like a credible explanation for these problems.

 

I am going to say no, but that is just a guess.

Did you clear those codes? I would suggest clearing them, then checking them again as soon as it starts running poorly.

 

I would guess the A2 code 1-2-3 and the A7 code 1-2-2 would be related to the coolant temp sensor and would have come up at similar times.


As firebird says, clear all the codes, drive around until it plays up and read the codes again.


The coolant temp sensor can make the car run funny, but we need to see if the codes come up again.