INTERMITTENT HESITATIONS, LOW POWER, & ROUGH RUNNING ENGINE. GMC Truck Sonoma Pickup

SUBJECT: INTERMITTENT HESITATIONS, LOW POWER, AND ROUGH RUNNING ENGINE IN COLD TEMPERATURES (REPLACE PCM)

MODELS: 1993-95 CHEVROLET AND GMC, M/L, S/T TRUCKS 1993-94 OLDSMOBILE BRAVADA WITH 4.3L ENGINE (VIN W - RPO L35) AND HYDRA-MATIC M30 AUTOMATIC TRANSMISSION ONLY

CONDITION:

SOME OWNERS MAY COMMENT ABOUT INTERMITTENT HESITATIONS AT AMBIENT TEMPERATURES BELOW -10 DEGREES C (14 DEGREES F). THE HESITATIONS MAY ALSO BE ASSOCIATED WITH LOW POWER OR A ROUGH RUNNING ENGINE. THIS CONDITION MAY LEAD TO A CLOSED THROTTLE STALL WHEN STOPPED. THIS CONDITION, IF ENCOUNTERED, WOULD MOST LIKELY OCCUR WITHIN THE FIRST FEW MINUTES OF ENGINE OPERATION AFTER A COLD OVERNIGHT SOAK. IF THE LOW POWER CONDITION WERE ENCOUNTERED, THE ENGINE WOULD RUN NORMALLY AFTER ONE VEHICLE IGNITION CYCLE (OFF/START/RUN).

CAUSE:

UNDER CERTAIN CONDITIONS A HIGH FREQUENCY TRANSIENT VOLTAGE SPIKE BACK FEEDS INTO THE ENGINE CONTROLLER (PCM) AND CAUSES IT TO RESET. PCM RESETS WOULD MANIFEST THEMSELVES AS A BUMP OR HESITATION. INFREQUENTLY THESE RESETS LEAD TO AN INCORRECT FUEL/SPARK RUN MODE WHICH IS ASSOCIATED WITH THE LOW POWER CONDITION.

CORRECTION:

REPLACE THE PCM WITH A NEW PCM. CHOOSE THE APPROPRIATE PCM FROM THE LIST BELOW.

YEAR MODEL PCM PART NUMBER 1993 M/L AND S/T 16245357 1994-95 M/L AND S/T 16245358

IN ADDITION TO REPLACING THE PCM, THE ASSOCIATED MEMCAL MUST ALSO BE REPLACED. CHOOSE THE APPROPRIATE MEMCAL FROM THE LISTED TABLES.

IMPORTANT: THE SERVICE MEMCAL IS COMMON WITH AN EGR SERVICE MEMCAL, AND SOME VEHICLES MAY ALREADY HAVE THE CORRECT SERVICE MEMCAL.

1993 4.3L (L35) MEMCAL LISTING NEW NEW PROM ID EMISSION NEW MEMCAL BROADCAST CODE (SCAN BODY STYLE TYPE AXLE PART NUMBER (PROM LABEL) TOOL)

M-VAN NA5/NA6 GU6(3.42) 16239362 BUZJ 9331 GT4(3.73)

M-VAN NB2 GU6(3.42) 16239338 BUZF 9311 GT4(3.73)

L-VAN NA5/NA6 GU6(3.42) 16239347 BUZH 9321 GT4(3.73)

L-VAN NB2 GU6(3.42) 16239323 BUZD 9301 GT4(3.73)

S/T PICKUP, NA5/NA6 GU4(3.08) 16239400 BUZM 9361 S/T UTILITY GU6(3.42) GT4(3.73)

T PICKUP, NB2 GU4(3.08) 16239376 BUZK 9341 S/T UTILITY GU6(3.42) GT4(3.73)

S PICKUP NB2 GU4(3.08) 16239397 BUZL 9351 GU6(3.42)

1994 4.3L (L35) MEMCAL LISTING

NEW BROADCAST NEW EMISSION NEW MEMCAL CODE PROM ID BODY STYLE TYPE AXLE PART NUMBER (PROM LABEL) (SCAN TOOL)

M-VAN NA5/NA6 GU6(3.42) 16239423 BUZY 9355 GU4(3.73)

M-VAN NB6 GU6(3.42) 16239408 BUZT 9315 GU4(3.73)

L-VAN NA5/NA6 GU6(3.42) 16239410 BUZU 9325 GT4(3.73)

L-VAN NB6 GU6(3.42) 16239412 BUZW 9335 GT4(3.73)

S/T PICKUP NA5/NA6 GU4(3.08) 16239406 BUZS 9305 NB2 GU6(3.42) GT4(3.73)

S/T UTILITY L35(NO GU4(3.08) 16239420 BUZX 9345 CTF) GU6(3.42) NA5/NA6/NB6 GT4(3.73)

S/T UTILITY L35(WITH GU6(3.42) 16239403 BUZR 9295 CTF) GT4(3.73) NF2/NB6

1995 4.3L (L35) MEMCAL LISTING

NEW BROADCAST NEW EMISSION NEW MEMCAL CODE PROM ID BODY STYLE TYPE AXLE PART NUMBER (PROM LABEL) (SCAN TOOL)

S/T UTILITY NF2/NB6 ALL 16239464 BWAK 9445

M-VAN NF2/NB6 GU5(3.23) 16239462 BWAJ 9435 GU6(3.42) GT4(3.73)

M-VAN VD1 GU6(3.42) 16239457 BWAF 9415 GT4(3.73)

L-VAN NF2/NB6 GU6(3.42) 16239459 BWAH 9425 GT4(3.73)

L-VAN VD1 GU6(3.42) 16239444 BWAD 9405 GT4(3.73)

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OPERATION: J-6360 LABOR TIME: 1993 M/L 0.6 HRS. S/T 0.8 HRS. ALL 1994 M/L 0.7 HRS. S/T 0.7 HRS. UTILITY 1994 S/T 1.2 HRS. PICKUP 1995 M/L 0.7 HRS. S/T 1.2 HRS. ALL

FIGURES: 0 ATTACHMENTS: 0

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.