CHECK ENGINE LIGHT CODE 34 DIAGNOSIS INFORMATION LISTED
VEHICLES AFFECTED: 1985 'A-J-and-X' Cars With LB6 2.8L MFI Engine (VIN Code W and 1985 'F' Cars With LB8 2.8L MFI Engine (VIN Code S)
Customer comments may be received on some 1985 cars with the 2.8L MFI engine regarding check engine light (code 34), engine surge, or engine hesitation. Listed below is some information that should help to correct each condition.
Item no. 1 - Check Engine Light (Code 34) ----------------------------------------- Code 34 will set if the following conditions are met:
Engine running
Mass Air Flow sensor (MAF) disconnected, faulty relay or MAF signal circuit shorted to ground.
OR
Air flow less than 2 grams per second (low frequency)
To correct a Code 34 check engine light, first make sure that the MAF relay is working and supplies + 12 volts to the MAF sensor. This can be accomplished by connecting a test light between ground and the '+' terminal of the MAF sensor harness. With the ignition 'on', the test light should light. If the light doesn't light, check for an open in the + 12 volt supply or a faulty relay.
If power is supplied to the MAF sensor, use the standard fault tree for check engine light (Code 34) in Section 6E3 of the Service Manual.
Item no. 2 - Engine Surqe Item no. 2A
If the vehicle exhibits surge, follow procedures in Section B - Symptoms, Section 6E3 of the Service Manual for diagnosing surge. Particular attention should be given to:
Checking rear spark plug wires for heat damaged wires. Replace if damaged.
Checking spark plug wire boots for evidence of carbon tracking. If carbon tracking is present in spark plug boot replace both spark plug and spark plug wire.
Item no. 2B
If the surge does not go away, update the following parts should correct the condition.
Install the latest PROM unless the vehicle already has it. (This can be done by using Chart I).
The lastest PROM has revised EGR scheduling when the torque converter is locked. This should reduce surge.
If the car is a Chevrolet Celebrity, Pontiac 6000 or Pontiac STE, install a new air cleaner housing which has a honey cell flow straightener. This is provided in a service kit (P/N 25097022) which contains the air cleaner housing, gasket, and clamp.
After installing this new housing the car should be parked and the engine allowed to cool to ambient temperature. Then it should be cold started and driven a minimum of three miles to update the ECM memory.
NOTICE: During the first cold start after installing the new air cleaner housing the engine may hesitate and possibly backfire until the ECM memory is updated.
Item no. 3 - Engine Hesitation
If the engine exhibits hesitations during accelerations when the engine is cold, update the following parts to correct the problem.
Install the latest PROM unless the vehicle already has it. (This can be done using Chart I).
If the vehicle has early production injectors, install the updated injectors which have a revised spray pattern. The updated injector is part of a kit P/N 17111297, (six (6)) kits required per engine.
NOTICE: Injectors with the correct spray pattern have already been installed on engines with a build date code of 0107 (January 7th) or later.
Example: T 01 07 CAF
This code is stamped on the horizontal machined surface of the block just forward of the intake manifold.
If the engine continues to exhibit a hesitation after the above updates, follow diagnostic procedures for hesitation in section B-Symptoms, Section 6E3 of the Service manual.
NOTICE: One of the steps in the Service Manual is to perform the injector balance test. It is important to run this test because this test will identify plugged injectors. If the injectors are plugged, clean the injectors using recommended service procedures in service Bulletin 85-6-245.
CHART I: PROCEDURE TO IDENTIFY AND INSTALL LATEST PROM Procedure --------- If scan tool is available, determine PROM I.D. using a scan tool, find scan data in column A of the following chart and perform action in column C.
If scan tool is unavailable, remove ECM from vehicle and determine PROM I.D. by visually inspecting PROM. Find PROM code in column B of the following chart and perform action in column C.
A B C AIR SCAN TOOL PROM I.D. SALES MODEL TRANS. AXLE COND. DATA IN VEHICLE ACTION ----- ----- ------ ---- ----- ---- ---------- ------- FED A A.T.(MD9) 2.84 Yes 6961 2412 CSH Install Service P/N 16049780 9381 9781 FPH NO ACTION
FED A A.T.(KD9) 2.84 No 3731 4726 DTK Install Service P/N 16052572 9721 2573 FRZ NO ACTION
FED A A.T.(KD9) 3.18 Yes 3741 4731 DTL Install Service P/N 16052577 9731 2578 FSA NO ACTION
FED A A.T.(KD9) 3.18 No 3751 4736 DTM Install Service P/N 16052584 9741 2585 FSB NO ACTION
FED A A.T.(ME9) 3.06 Yes 3761 4568 DTN Install Service P/N 16049936 9751 9937 FSC NO ACTION
FED A A.T.(ME9) 3.06 No 3771 4577 DTP Install Service P/N 16049942 9761 9943 FSD NO ACTION
FED A-STE A.T.(KD9) 3.18 Yes 8051 8145 FCN Install Service P/N 16049719 0001 9720 FTK NO ACTION
FED A-POLI A.T.(MD9) Yes 3781 4584 DTR Install Service P/N 16049947 9771 9948 FSF NO ACTION
FED A-POLT A.T.(KD9) No 3791 4603 DTS Install Service P/N 16049953 9781 9954 FSH NO ACTION
FED A A.T.(KD9) 2.84 Yes 3801 4614 DTT Install Service P/N 16052588 9791 2589 FSJ NO ACTION
FED A A.T.(KD9) 2.84 No 3811 4620 DTU Install Service P/N 16049964 9801 9965 FSK NO ACTION
FED A A.T.(MD9) 3.18 Yes 3821 4625 DIV Install Service P/N 16052594 9811 2595 FSL NO ACTION
FED A A.T.(KD9) 3.18 No 3831 4636 DTX Install Service P/N 16052639 9821 2640 FSM NO ACTION
FED A A.T.(ME9) 3.06 Yes 3841 4646 DTY Install Service P/N 16049647 9831 9648 FSN NO ACTION
FED A A.T.(ME9) 3.06 No 3851 4787 DTZ Install Service P/N 16049653 9841 9654 FSP NO ACTION
FED J A.T.(KD9) 3.18 Yes 8481 2643 CXK Install Service P/N 16049816 9481 9817 FPU NO ACTION
FED J A.T.(MD9) 3.18 No 8491 2648 CXN Install Service P/N 16049822 9491 9823 FPW NO ACTION
FED, J M4 3.65 Yes 8521 2503 CXS Install Service P/N 16052043 9521 2044 FPZ NO ACTION
FED J M4 3.65 No 8531 2508 CXT Install Service P/N 16052087 9531 2088 FRA NO ACTION
FED X A.T.(KD9) 2.84 Yes 6981 2603 CSK Install Service P/N 16052542 9401 2543 FPK NO ACTION
FED X A.T.(MD9) 2.84 No 3861 4797 DUA Install Service P/N 10652598 9851 2599 FSR NO ACTION
FED X A.T.(MD9) 3.18 Yes 3871 4741 DUB Install Service P/N 16052603 9861 2604 FSS NO ACTION
FED X A.T.(MD9) 3.18 No 3881 4746 DUC Install Service P/N 16049669 9871 9670 FST NO ACTION
FED F-CHV A.T.(MDB) 3.42 Yes 7021 2613 CSP Install Sorvice P/N 16049803 9441 9804 FPP NO ACTION
FED F-CHV A.T.(MD8) 3.42 No 3581 4666 DSR Install Service P/N 16049838 9571 9839 FRF NO ACTION
FED F-PONT A.T.(ND8) 3.45 Yes 3591 4671 DSS Install Service P/N 16049844 9581 9845 FRH NO ACTION
FED F-PONT A.T.(MD8) 3.45 No 3601 4676 DST InstailL Sevice P/N 16049849 9591 9850 FRJ NO ACTION
FED F-CHV M.T.(NB1) 3.42 Yes 7041 8555 CSS Install Service P/N 16052034 9461 2035 FPS NO ACTION
FED F-CHV M.T.(KBI) 3.42 No 3611 8559 DSU Install Service P/N 16052056 9601 2057 FRK NO ACTION
FED F-PONT M.T.(MBI) 3.45 Yes 3621 8548 DSW Install Service P/N 16052060 9611 2061 FRL NO ACTION
FED F-PONT M.T.(KBI) 3.45 No 3631 8547 DSX Install Service P/N 16052065 9621 2066 FRK NO ACTION
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
