OBD I Code 18 1993 3800 for 1993 Buick LeSabre

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    Anonymous

    1993 Buick LeSabre 3800 323K+ miles.

    Problems first with car happen last summer with the car cutting off after being operated; could drive approximately six miles and it would cut off but not start again until engine was cool. No codes were set. At that time the crank position sensor, the cam sensor, the coolant sensor, the ignition control module and the mass air flow sensor was replaced. Replacing the MAF fixed the problem and the car ran great for a few months.

    Then back at the start of winter, I started the car one morning to allow it to warm the interior before driving. When I went to leave, the car was idling rough and the check engine light was lit. Checking the code revealed Code 18 set. I obtain the GM shop manual and went through the list of troubleshooting without any luck, all circuits appeared to be OK and the cam signal pulsed between 0 and 5 volts. I could not find any fault. I decided to replace the new CKP sensor just in case it was malfunctioning. I also decided to replace the timing chain and gears since the engine had such high mileage on it.

    The timing had not jump when I went into the engine. The harmonic balance rings were as they should be. The car started well after these repairs but the rough idle was still present and the check engine light soon illuminated. The Code 18 error is still there but it is now joined by a code 17.

    Shop manuals are fine but sometimes other things happen that the manuals don’t cover. I am hoping that someone can help me to determine the problem so I can get my old Buick back on the road.

  • #14397 Reply

    Protech

    REPLY: So, you’ve got a spark reference circuit code and a cam/CRANK code. How long ago did you replace the sensors? Did you use aftermarket or GM parts? Any of these could have gone bad again. Hard to pinpoint without actual diagnosis, but it could be a bad ignition module, crank sensor, or even a faulty computer. You might want to check the wiring to each of those sensors as well for any chaffing or bare wires.

    Thanks for the reply. I have a GM Shop manual for this car. The car sat for several days with the interior lights on and I had to remove the BATTERY to charge it. After charging the battery and inserting it in the car I performed the diagnostics for the Code 17. The “Spark Reference Circuit” checked out OK, including all the voltage tests at the PCM connector. The voltage from the crank sensor was 5 volts as per the manual. I started the car with the probe at the PCM connector and the voltage differed between 1.x and 3 volts and finally stabilised at 3 volts as per the information in the manual. After completing the tests for Code 17 I checked the codes stored in the computer and the Code 17 was gone and it has not returned. However, Code 18 remains.

    Yes, I am using aftermarket sensors as they are the only ones available locally for this older car.

    I replaced the crank position sensor twice now. The Cam position sensor is working. I checked for the 5 volts at the PCM BA12 connector and it was 5 volts when the cam interrupter magnet was off the cam sensor and 0 volts when the interrupter was under the cam sensor. The fuel control voltage was also present at the PCM. I switched out the new ignition control module with the original ICM and there was no change. The vanes on the harmonic balancer are all as they should be, none are bent, none are missing.

    I did continuity tests from the PCM connector to the sensors to the ignition control module and found no open circuits. I tested the ground between the ICM Module by placing an OHMMETER probe on the top exposed metal that one sees between the coils and the alternator housing and there was a good solid ground.

    I did managed to obtain a scan tool temporary when the error first occurred. I could not allow the engine to come to operating temperatures because the engine started idling so rough I was afraid of damaging something if I allow it to continue running. The scan information is below; the first was obtain without waiting for the engine to warm to operating temperatures and the second was done as warm as I could get with a rough idling engine. I hope that some help can be provided to solve this Code 18 issue as this is the only vehicle I have to drive.

    LT Fuel Trim: 128

    LT Fuel TR CL: 5

    Evap Solenoid: off

    EGR Sol all of them off

    KS Counter: 1

    Exhaust O2: Lean

    IAC Position: 140

    Idle Req RPM: 1288

    ST Fuel Trim: 128

    Knock RET: 0

    Loop Status: OPEN

    MAF (sr/S): 3708

    IAT (degrees F): 53

    O2S (mV): 466

    O2S CROSSCNTS: 54

    PROM ID: 1284

    QUAD DRIVER 1: OK

    QUAD DRIVER 2: OK

    Spark Adv: (degrees): 23

    LT Fuel Trim: 135

    LT Fuel TR CL: 5

    Evap Solenoid: off

    Coolant Temp (F): 114

    EGR Sol all of them off

    KS Counter: 13

    Exhaust O2: Rich

    IAC Position: 103

    Idle Req RPM: 1050

    ST Fuel Trim: 128

    Knock RET: 0

    Loop Status: OPEN

    MAF (sr/S): 2791

    IAT (degrees F): 52

    O2S (mV): 955

    O2S CROSSCNTS: 54

    PROM ID: 1284

    QUAD DRIVER 1: OK

    QUAD DRIVER 2: OK

    Spark Adv: (degrees): 7

    REPLY: Your first mistake is using aftermarket parts on the car. There has to be a GM dealer somewhere in your area. If that is not an option, call a GM dealer and get the part numbers and go to a factory authorized AC Delco parts center and get the factory stuff. All your tests seem ok, but something is glitching out. Unless you have known good GM parts on the car, you’re at a standstill.

    Yes, I might could find ACDelco on the internet. However, the sensors seem to be doing their job. I checked again today for loose connectors, open or shorted circuits and found none. If the ICM is taking readings from the cam and crank sensors and putting the correct voltage out to the PCM, then they are functioning even if they are aftermarket parts. I removed the battery cable while I was working. When I finished checking out everything, I attached the battery cable and started the engine. The same rough idle and surging a few times then the check engine light comes on. I don’t think the car idled for even a minute before I got the check engine light.

    With the code 17 appearing to only disappear and this unexplained code 18 I can not seem to find a cause for, is it possible the PCM could be at fault? It is the original one and is 19 years old.

    REPLY: It is very possibly a faulty PCM, which I said in my first reply to you. These are difficult to diagnose being OBD1 since you can’t see as much information on the scanner like you can on an OBD2 system. If you’re certain the wiring is good, sensors are working correctly, other things like injector function and fuel/air delivery are fine, as well as a free flowing exhaust/egr system…then yes, I’d say try a new computer.

    New computer did not solve the problem. Code 18 still exists. Can a bad PROM cause this?

    I have followed the steps in the GM shop manual, and can find no faulty wires. Two new crank position sensor, new cam sensor, new ICM.

    I think the car is running rough due to this Code 18 cam/crank error (not a fault, but an error). Is bad wiring the only thing that can cause this?

    REPLY: There you go thinking again! LOL, but seriously I’m fresh out of ideas….anything is possible, bad PROM, wiring, or some other reason the car is running rough…fuel, ignition, injectors, just plain worn out, etc, etc…Did you ever think that you may have a mechanical problem actually setting that code? The cam can wear out, become flat, etc…the crank can get too much play in it to keep the timing correct for the sensor. With the amount of miles on the car, this could in fact be the problem and internal engine repair might be necessary. Unfortunately, it’s time to bring it to a shop and have a more qualified person than you look at it, or just dump the car. This now ends your free help!

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