REPLACEMENT OF ISOLATION DIODES. Chevrolet Impala 1983

REVISION 06/30/92

THIS BULLETIN IS BEING REVISED TO INCLUDE THE 1992 MODEL YEAR

REVISION 04/09/93

THIS BULLETIN IS BEING REVISED TO INCLUDE THE 1993 MODEL YEAR AND REVISE THE GMSPO PART NUMBERS FOR BOTH DIODE APPLICATIONS. THE PART NUMBER REVISIONS WILL ALSO UPDATE CERTAIN 1993 SERVICE MANUALS (SECTION 8A).

THE DIODE PART NUMBERS WERE REVISED AGAIN. INSTEAD OF THE DE PART NUMBERS (16020519 AND 16011840) FOR THE TWO GMSPO DIODES, THE PART NUMBERS WILL ORIGINATE FROM PACKARD ELECTRIC. THE RATING OF THESE DIODES HAS ALSO CHANGED AND ARE LISTED IN THE CHART BELOW.

REVISION 04/21/93

THIS BULLETIN IS BEING REVISED TO CHANGE THE PART AVAILABILITY DATE OF P/N 12112422 TO MAY 10, 1993.

REVISION: 09/01/94

THIS BULLETIN IS BEING REVISED FOR GENERAL MOTORS OF CANADA ONLY TO CORRECT DUPLICATE GM OF CANADA BULLETIN NUMBERS. PLEASE DISCARD GM OF CANADA BULLETIN #93-8B-109 ISSUED ON SEPTEMBER 30, 1993. ----------------------------------------------------------------------

SUBJECT: INFORMATION ON REPLACEMENT OF ISOLATION DIODES

MODELS: 1993 AND PRIOR PASSENGER CARS AND TRUCKS

MANY OF THE ELECTRICAL SYSTEMS ON OUR VEHICLES USE A DIODE TO ISOLATE CERTAIN CIRCUITS AND PROTECT THEM FROM VOLTAGE SPIKES. SOME OF THE CIRCUITS WHICH MAY USE SUCH A DIODE ARE LISTED BELOW:

* A/C COMPRESSOR CLUTCH * ABS/4WAL NOTE: THE ABS DIODE ON THE DELCO MORAINE SYSTEM IS HIDDEN INSIDE OF AN ELECTRICAL CONNECTOR UNDER THE CARPET AT THE RIGHT KICK PANEL. * WIPER * CHARGING SYSTEM (HIDDEN IN WIRE HARNESS) * PARKING BRAKE (VEHICLES WITH ABS) * RELAYS * SOLENOIDS * DIESEL GLOW PLUG CIRCUIT * DAY TIME RUNNING LIGHTS

OBTAINING REPLACEMENT DIODES CAN SOMETIMES BE A PROBLEM. A UNIVERSAL DIODE, THAT MEETS THE SPECIFICATIONS IN THE CHART BELOW, MAY BE USED FOR THE APPLICATIONS LISTED ABOVE. SINCE CERTAIN DIODE APPLICATIONS HAVE SPECIFIC PART NUMBERS, ALWAYS REFERENCE THE APPLICABLE GM PARTS CATALOGUE BEFORE INSTALLING ONE OF THE UNIVERSAL DIODES LISTED IN THIS BULLETIN.

WHEN INSTALLING THE NEW DIODE, USE THE FOLLOWING PROCEDURES TO OBTAIN A LASTING REPAIR:

1. IF THE DIODE IS TAPED TO THE HARNESS, REMOVE ALL OF THE TAPE.

2. PAYING ATTENTION TO CURRENT FLOW DIRECTION, REMOVE INOPERATIVE DIODE FROM THE HARNESS WITH A SUITABLE SOLDERING TOOL. IF THE DIODE IS LOCATED NEXT TO A CONNECTOR TERMINAL, REMOVE THE TERMINAL(S) FROM THE CONNECTOR TO PREVENT DAMAGE FROM THE SOLDERING TOOL.

3. CAREFULLY STRIP AWAY A SECTION OF INSULATION NEXT TO THE OLD SOLDERED PORTION OF THE WIRE(S). DO NOT REMOVE ANY MORE THAN IS NEEDED TO ATTACH THE NEW DIODE.

4. CHECK CURRENT FLOW DIRECTION OF THE NEW DIODE, BEING SURE TO INSTALL THE DIODE WITH CORRECT BIAS. REFERENCE THE APPROPRIATE SERVICE MANUAL WIRING SCHEMATIC TO OBTAIN THE CORRECT DIODE INSTALLATION POSITION. REFERENCE FIGURE 1 FOR REPLACEMENT DIODE SYMBOLS AND CURRENT FLOW EXPLANATIONS.

ATTACH THE NEW DIODE TO THE WIRE(S) USING 60/40 ROSIN CORE SOLDER. USE A HEAT SINK (ALUMINUM ALLIGATOR CLIP) ATTACHED ACROSS THE DIODE WIRE ENDS TO PROTECT THE DIODE FROM EXCESS HEAT. FOLLOW THE MANUFACTURER'S INSTRUCTIONS FOR THE SOLDERING EQUIPMENT YOU ARE USING.

5. INSTALL TERMINAL(S) INTO THE CONNECTOR BODY IF PREVIOUSLY REMOVED IN STEP NUMBER 2.

6. TAPE THE DIODE TO THE HARNESS OR CONNECTOR USING ELECTRICAL TAPE. TO PREVENT SHORTS TO GROUND AND WATER INTRUSION COMPLETELY COVER ALL EXPOSED WIRE AND DIODE ATTACHMENT POINTS.

NOTE: A UNIVERSAL DIODE WITH A 3 AMP, 400 PIV (PEAK INVERSE VOLTAGE) RATING CAN BE USED IN ALL OF THE PREVIOUSLY MENTIONED APPLICATIONS.

DIODE BRAND RATING NUMBER P/N COMMENTS ----------- ------------- --- --------- GMSPO 1N4004 12112421 1 AMP, 400 PIV - ALL RADIO SHACK 276-1103 APPLICATIONS EXCEPT A/C COMPRESSOR CLUTCH

GMSPO 1N5404 12112422 3 AMP, 400 PIV - A/C RADIO SHACK 276-1144 COMPRESSOR CLUTCH APPLICATION

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

THE FOLLOWING 1993 SERVICE MANUALS WILL NEED TO BE UPDATED WITH THE CORRECT PART NUMBERS AND RATING CHANGES.

CARLINE PAGE

ALL J, L, N, A, W, AND 8A-5-12 U0

HEAT SINK, PART NUMBER 276-1567, CAN BE OBTAINED FROM RADIO SHACK.

WE BELIEVE THE DIODES AND HEAT SINK LISTED IN THIS ARTICLE AS WELL AS THEIR MANUFACTURER TO BE RELIABLE. THERE MAY BE ADDITIONAL MANUFACTURERS OR EQUIVALENT PRODUCTS. GENERAL MOTORS DOES NOT ENDORSE, INDICATE ANY PREFERENCE FOR OR ASSUME ANY RESPONSIBILITY FOR THE PRODUCTS FROM THESE FIRMS OR FOR ANY SUCH ITEMS WHICH MAY BE AVAILABLE FROM OTHER SOURCES.

FIGURES: 01

Object Number: 81251 Size: FS

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.