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Engine Diagnostic Codes: To do a diagnostic on engine codes you take a paper clip and connect terminal (A) and (B) together. A Code 12 will flash on the Check Engine light 3 times first and then give you any additional codes if present. A code is displayed for example 12 (1 flash, pause, 2 flashes). Listed below is a list of all the available codes and what they mean.

Trouble Codes	Circuit or System	Probable Cause
Code 12	No distributor reference pulses to the ECM	This code will flash whenever the diagnostic terminal is grounded with the ignition turned On and the engine not running. If additional trouble codes are stored in the ECM then they will appear after this code has flashed 3 times. If this code appears while the engine is running, no reference pulses from the distributor are reaching the ECM.
Code 13	Oxygen sensor circuit	Check for a sticking or misadjusted throttle position sensor. Check the wiring and connectors from the oxygen sensor. Replace the oxygen sensor.
Code 14	Coolant sensor/High temp	If the engine is experiencing overheating problems the problem must be rectified before continuing. Check all wiring and connector associated with the coolant temperature sensor. Replace the coolant temperature sensor.
Code 15	Coolant sensor/Low temp	See Above, then check the wiring connections at the ECM.
Code 21	Throttle position sensor/ voltage high	Check for a sticking or misadjusted TPS plunger. Check all wiring and connections between the TPS and the ECM. Adjust or replace the TPS. (see other instructions on doing this)
Code 22	Throttle position sensor/ voltage low	Check TPS adjustment. Check the ECM connector. Replace the TPS.
Code 23	MAT low temp indication	Sets if the Manifold Air Temperature (MAT) sensor, connections or wires are open for 3 seconds.
Code 24	Vehicle speed sensor	A fault in this circuit should be indicated only when the vehicle is in motion. Disregard if it is set when the drive wheels are not turning. Check the connections at the ECM. Check the TPS setting.
Code 25	ATI sensor/high air	High temperature indication. Sets if the sensor or signal line becomes grounded for 3 seconds.
Code 31	Wastegate Overboost
Code 32	EGR	Vacuum switch shortened to ground on start-up, switch not closed after the ECM has commanded the EGR for a specified period of time or the EGR solenoid circuit is open for a specified period of time. Replace the EGR valve.
Code 33	MAP sensor	Check the vacuum hoses from the MAP sensor. Check the electrical connections at the ECM. Replace MAP sensor.
Code 34	Vacuum sensor or MAP sensor	This will set when the signal voltage from the MAP sensor is too low. Instead the ECM will substitute a fixed MAP value and use the TPS to control fuel delivery. Replace the MAP sensor.
Code 35	IAC valve	Idle Air Control error. Code will set when closed throttle speed is 50 rpm above or below the correct idle speed for 30 seconds. Replace the IAC.
Code 42	Electronic Spark Timing (EST)	This code is when this circuit is grounded or open. A malfunctioning HEI module can cause this code.
Code 43	Electronic Spark Control (ESC)	The ESC retard signal has been on for too long or the system has failed a functional check.
Code 44	O2/Lean exhaust	Check the ECM wiring connections, particularly terminals 8 and 15. Check for vacuum leakage at the TBI base gasket, vacuum hoses or the intake manifold gasket. Replace the oxygen sensor.
Code 45	O2/Rich exhaust	Check the evaporative charcoal canister and its components for the presence of fuel. Replace the oxygen sensor.
Code 51	PROM or MEM-CAL	Make sure the PROM or MEM-CAL is properly installed in the ECM. Replace the PROM or MEM-CAL.
Code 52	CALPAK	Check the CALPAK to insure proper installation. Replace the CALPAK.
Code 53	System over-voltage (indicates a basic alternator problem)	Check charging system.
Code 54	Fuel Pump	Low fuel pump voltage. Sets when the fuel pump voltage is less than 2 volts when reference pulses are being received.
Code 55	ECM	Be sure that the ECM ground connections are tight. If they are, replace the ECM.

4-Wheel Anti-Lock Diagnostic Codes:

To do a diagnostic on 4WAL codes you take a paper clip and connect terminal (A) and (H) together. After 20 seconds if any codes are present they will be displayed by the flashing of the Anti-Lock light. A code is displayed for example 12 (1 flash, pause, 2 flashes). Listed below is a list of all the available codes and what they mean.

To clear the code from the ECU memory, with the ignition On, place the jumper between (A) and (H) for two seconds, remove for one second, and replace again for two seconds. The Antilock/Brake light should light, then go off.

Note: How Codes 86 and 88 work if the problem exist, I don't know, I am just passing the info from the manual.

Trouble Codes	Circuit or System	Probable Cause
Code 21	Right Front Wheel Circuit	Faulty wheel sensor or open circuit.
Code 22	Right Front Wheel Circuit	No signal. Remove the wheel. Check for a damaged sensor or loose electrical connectors.
Code 23	Right Front Wheel Circuit	Intermittent signal, indicating a loose electrical connector.
Code 25	Left Front Wheel Circuit	No signal. Remove the wheel. Check for a damaged sensor or loose electrical connectors.
Code 26	Left Front Wheel Circuit	Intermittent signal, indicating a loose electrical connector.
Code 27	Left Front Speed Sensor Circuit	Faulty sensor or loose electrical connector.
Code 28	Speed Sensor Signal	Erratic brake action at low speeds and pedal pressures indicates a fault in the speed sensor circuit or speedometer.
Code 29	EHCU Circuit	A loss of signal from all four sensors indicates a loose EHCU connector.
Code 31	Right Rear Speed Sensor Circuit	An intermittent code indicates a loose electrical connector.
Code 32	Right Rear Wheel Circuit	No signal. Remove the wheel. Check for a damaged sensor or loose electrical connectors.
Code 33	Right Rear Wheel Circuit	Intermittent signal, indicating a loose electrical connector.
Code 35	Left Rear Wheel Circuit	Intermittent signal, indicating a loose electrical connector.
Code 36	Left Rear Speed Sensor Circuit	No signal. Remove the wheel. Check for a damaged sensor or loose electrical connectors.
Code 37	Left Rear Speed Sensor Circuit	An inconsistent anti-lock action at low speeds and pedal pressure is a sign of a fault in the speed sensor unit or connectors.
Code 38	EHCU valve circuit	A pulsing pedal indicates a defective wheel sensor or faulty EHCU valve.
Code 41 through 66	4WAL control unit or motor circuit	Check for a loose ground connection at the motor circuit. Clear the code and drive the vehicle. If any of these codes return, the EHCU valve may be faulty.
Code 67	Motor circuit	Check the motor for loose electrical connections.
Code 68	Motor circuit	A locked motor or an open circuit. Check the motor for loose electrical connections.
Code 71 through 74	4WAL control unit	Clear the code and drive the vehicle. If any of these codes return, the EHCU valve may be faulty.
Code 81	Brake switch circuit	Make sure the driver hasn't been riding the brake. Check the brake switch adjustment and electrical connections
Code 86	Anti-Lock warning light	Check the light and wiring for a short circuit.
Code 88	Brake warning light	Check the light and wiring for a short circuit.