a multi meter and a few logical tests should locate and isolate the problem source,
Id be checking the fuses and of course it helps to have access to your vehicle shop manual
start with verifying battery voltage and that all the fuses are good then logically trace the current through the ignition.
be sure its not a vats anti-theft system issue, or ignition switch issue, and if you have a code reader check trouble codes
http://garage.grumpysperformance.co...-system-vats-making-you-crazy.520/#post-45049
http://garage.grumpysperformance.co...ouble-shooting-rebuilding-hei-ignitions.2798/
http://garage.grumpysperformance.com/index.php?threads/vats-fuse.3453/#post-42500
http://garage.grumpysperformance.co...n-jumping-in-with-both-feet.14918/#post-84129
http://garage.grumpysperformance.co...oven-facts-if-your-in-doubt.13051/#post-84890
http://garage.grumpysperformance.co...r-just-start-swapping-parts.15880/#post-95388
http://garage.grumpysperformance.co...to-locate-a-problems-source.14297/#post-73009
http://garage.grumpysperformance.com/index.php?threads/starter-circuit-related-info.676/#post-937
http://garage.grumpysperformance.com/index.php?threads/vats-fuse.3453/#post-42500
https://www.lifewire.com/what-is-car-code-reader-534869
https://repairpal.com/gm-obd-i-code-chart
GM OBD I Trouble Code Chart
Code Description
Code 12 No distributor reference pulse (diagnostic test active)
Code 13 Oxygen sensor circuit open or no activity
Code 14 Engine coolant temp sensor error (high temp indicated)
Code 15 Engine coolant temp sensor error (low temp indicated)
Code 16 System voltage too low
Code 17 Camshaft position sensor error
Code 21 Throttle position sensor error (signal high)
Code 22 Throttle position sensor error (signal low)
Code 23 Intake air temp sensor error (low temp indicated)
Code 24 Vehicle speed sensor error (open circuit or no activity)
Code 25 Intake air temp sensor error (high temp indicated)
Code 26 Quad Driver Module (QDM A) error
Code 28 Auto transmission range pressure switch error
Code 31 Wastegate solenoid circuit error
Code 31 Gear Position Switch (PRNDL) error
Code 32 Baro sensor circuit error / EGR circuit Error / MAP sensor signal open
Code 33 MAP sensor circuit error (signal high indicating low vacuum)
Code 34 MAP sensor circuit error (signal low indicating high vacuum)
Code 35 IAC problem or idle error
Code 36 MAF sensor error / 24x crankshaft position sensor circuit error / 4T60-E Shifting error
Code 37 TCC brake switch circuit error
Code 38 TCC brake switch circuit error
Code 39 Clutch switch circuit error / Torque converter clutch error
Code 41 Ignition control error / MEM-CAL error / C³I Cam Sensor Signal error
Code 42 Ignition bypass circuit error
Code 43 Knock sensor error
Code 44 Oxygen sensor error (lean condition indicated)
Code 45 Oxygen sensor error (rich condition indicated)
Code 46 Pass-Key II (VATS) system error - circuit out of freq range
Code 47 UART (serial data) circuit error
Code 51 PROM error / Incorrect MEM-CAL
Code 52 Fuel cal-pak incorrect or missing
Code 53 System voltage too high
Code 53 Digital EGR valve solenoid 1 error
Code 54 Fuel pump circuit low voltage / Digital EGR valve solenoid 2 error
Code 55 ECM error / Digital EGR valve solenoid 3 error
Code 56 Quad Driver Module (QDM B) error
Code 57 Boost control error
Code 58 Trans fluid temp sensor circuit error (low voltage) / VATS system error
Code 59 Trans fluid temp sensor circuit error (high voltage)
Code 61 A/C system performance
Code 63 Right bank O2 sensor circuit error / MAP sensor circuit signal voltage high (low vacuum indicated)
Code 64 Right bank O2 sensor lean exhaust indicated / MAP sensor circuit signal voltage low (high vacuum indicated)
Code 65 Right bank O2 sensor rich exhaust indicated
Code 66 A/C pressure sensor circuit error (low pressure indicated)
Code 67 A/C pressure sensor circuit error
Code 68 A/C clutch relay circuit error (shorted to ground)
Code 69 A/C clutch relay circuit error (open circuit indicated) / A/C high pressure switch error
Code 70 A/C pressure sensor circuit error (high pressure indicated)
Code 71 A/C evaporator temp sensor circuit error (low temp indicated)
Code 72 VSS signal circuit error
Code 73 A/C evaporator temp sensor circuit error (high temp indicated)
Code 75 Digital EGR solenoid #1 circuit error
Code 76 Digital EGR solenoid #2 circuit error
Code 77 Digital EGR solenoid #3 circuit error
Code 79 Transmission fluid over temp
Code 80 Transmission component slipping
Code 82 3x crankshaft position sensor circuit error
Code 85 PROM error
Code 86 ECM Analog/Digital error
Code 87 EEPROM error (flash memory error)
Code 90 TCC error
Code 93 Transmission pressure control solenoid circuit error
Code 96 Transmission system voltage low
Code 98 Invalid PCM program
Code 99 Invalid PCM program
1985 to 1991 Computer Codes
Code #12: Normal No Codes.
Code #13: Open Oxygen Sensor Circuit.
Code #14: Coolant Sensor Circuit Low.
Code #15: Coolant Sensor Circuit High.
Code #21: Throttle Position Sensor High.
Code #22: Throttle Position Sensor Low.
Code #23: Manifold Air Temperature Circuit High.
Code #24: Vehicle Speed Sensor.
Code #25: Manifold Air Temperature Circuit Low.
Code #32: EGR System Failure.
Code #33: Mass Air Flow Sensor High.
Code #34: Mass Air Flow Sensor Low.
Code #36: Mas Air Flow Sensor Burn-Off Function Fault.
Code #41: Cylinder Select Error.
Code #42: Electronic Spark Timing.
Code #43: Electronic Spark Control.
Code #44: Lean Exhaust indication.
Code #45: Rich Exhaust Indication.
Code #46: Vehicle Anti Theft Fault.
Code #51: Faulty Mem-Cal.
Code #52: Fuel Calpak Missing.
Code #52: (1990-91 Corvette Only): Engine Oil Temperature Sensor Low.
Code #53: System Over Voltage.
Code #54: Fuel Pump Circuit Low Voltage.
Code #55: Defective ECM.
Code #62: Engine Oil Temperature Sensor Circuit High.
1994 to 1996 DTC Computer Codes
DTC #11: Malfunction Indicator Lamp Circuit.
DTC #13: Bank #1 Heated Oxygen Sensor #1 Circuit:
DTC #14: Engine Coolant Temperature Sensor Circuit Voltage Low.
DTC #15: Engine Coolant Temperature Sensor Circuit Voltage High.
DTC #16: Distributor Ignition System Low Pulse.
DTC #18: Injector Circuit.
DTC #21: Throttle Position Sensor Circuit Voltage High.
DTC #22: Throttle Position Sensor Circuit Voltage Low.
DTC #23: Intake Temperature Sensor Circuit Voltage High.
DTC #24: Vehicle Speed Sensor Circuit.
DTC #25: Intake Air Temperature Sensor Circuit Voltage Low.
DTC #26: Evaporative Emission Canister Purge Solenoid Valve Circuit.
DTC #27: EGR Vacuum Control Signal Solenoid Valve Circuit.
DTC #28: Transmission Range Pressure Switch Assembly Fault.
DTC #29: Secondary Air Injection Pump Circuit.
DTC #32: Exhaust Gas Recalculation.
DTC #33: Manifold Absolute Pressure Sensor Circuit High.
DTC #34: Manifold Absolute Pressure Sensor Circuit Low.
DTC #36: Distributor Ignition System High Pulse.
DTC #37: Brake Switch Stuck On.
DTC #38: Brake Switch Stuck Off.
DTC #41: Ignition Control Circuit Open.
DTC #42: Ignition Control Circuit Shorted.
DTC #43: Knock Sensor Circuit.
DTC #44: Bank 1 LF Heated Oxygen Sensor #1 Circuit Lean.
DTC #45: Bank 1 LF Heated Oxygen Sensor #1 Circuit Rich.
DTC #47: Knock Sensor Circuit Or Module Missing.
DTC #48: Mass Air Flow Sensor Circuit.
DTC #50: System Voltage Low.
DTC #51: EEPROM Programming Error.
DTC #52: Engine Oil Temperature Sensor Circuit Voltage Low.
DTC #53: System Voltage Low.
DTC #55: Fuel Lean Monitor.
DTC #58: Transmission Fluid Temperature Sensor Circuit Low.
DTC #59: Transmission Fluid Temperature Sensor Circuit High.
DTC #62: Engine Oil Temperature Sensor Circuit Voltage Low.
DTC #63: Bank 2 RF Heated Oxygen Sensor #1 Circuit Open.
DTC #64: Bank 2 RF Heated Oxygen Sensor #1 Circuit Lean.
DTC #65: Bank 2 RF Heated Oxygen Sensor #1 Circuit Rich.
DTC #66: A/C Refrigerant Pressure Sensor Circuit Open.
DTC #67: A/C Pressure Sensor Circuit Sensor or A/C Clutch.
DTC #68: A/C Relay Circuit.
DTC #69: A /C Clutch Circuit.
DTC #70: A/C Clutch Relay Driver Circuit.
DTC #72: Vehicle Speed Sensor Loss.
DTC #73: Pressure Control Solenoid Circuit Current Error.
DTC #74: Traction Control System Circuit Low.
DTC #75: Transmission System Voltage Low
DTC #77: Primary Cooling Fan Relay Control Circuit.
DTC #78: Secondary Cooling Fan Relay Control Circuit.
DTC #79: Transmission Fluid Overtemp.
DTC #80: Transmission Component Slipping.
DTC #81: Transmission 2-3 Shift Solenoid Circuit.
DTC #82: Transmission 1-2 Shift Solenoid Circuit.
DTC #83: Torque Converter Solenoid Voltage High.
DTC #84: 3-2 Control Solenoid Circuit.(Auto Only).
DTC #84: 2nd And 3rd Gear Blockout Relay Control Circuit.
DTC #85: Transmission TCC Stock On.
DTC #90: Transmission TCC Solenoid Circuit.
DTC #91: One To Four Upshift Lamp(Manual Only).
DTC #97: VSS Output Circuit.
DTC #98: Tachometer Output Signal Voltage Wrong.
https://mechanicbase.com/trouble-code/obd1-codes/
Pinout of the OBD1 connector
- A = Ground
- B = Diagnosis Terminal
- C = A.I.R
- D = Service engine soon light
- E = Serial Data
- F = T.C.C
- G = Fuel pump
- H = Brake Speed input
- J = None
- K = None
- L = None
- M = Serial Data
How to read the codes:
- Always connect a car battery charger to your car when doing any electrical works that require the ignition on. Low voltage can cause a lot of trouble with the troubleshooting and a lot of error codes that we do not want.
- Put a jumper wire between PIN A and PIN B.
- Let the jumper wire sit there and turn the ignition to ON. Do not start the engine
- The Check engine light will begin to flash. Count the flashes. There will be a longer pause between the codes if you have several trouble codes and a shorter pause between the digits of the trouble codes. For example code 16 = 1 flash * Pause * 6 flashes.
- When all trouble codes are outputted, it will flash the code 12 – 1 flash * Pause * 2 flashes.
- Write down all the trouble codes numbers you got and check the trouble code table further down in the article.
- Remove the jumper wire and car battery charger.
I found this related info posted elseware
I'm going to assume your engine has a large cap HEI distributor...looks like this:
Locate the single, pink wire going into the side of the distributor cap (not the one shown in the image)
The pink wire in question is coming from the ignition switch.
The pink wire in question should have 12-volts with the key ON.
The pink wire should have 0-volts with the key OFF.
With the key OFF and the engine OFF, unplug the pink wire from the distributor. Using a volt meter or test light, probe the wire.
The meter/test light should show zero volts/light off.
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