Locate the Assembly Line Data Link (ALDL) port. It is located on the bottom side of the dash on the passenger side.

With the ignition OFF, jumper the A&B terminals on the ALDL port. (You can use a paperclip, wire, or ALDL Jumper Key).

With the ALDL A&B terminals jumped, turn ignition switch to ON position - DO NOT START THE MOTOR!

Now, focus onto your gauge cluster and count the flashes on the "CHECK ENGINE" or "SERVICE ENGINE" light. A Code 12 will flash on the Check Engine light 3 times first and then give you any additional codes if present. Code 12 will look like this:

FLASH, pause, FLASH, FLASH = code 12

If your ECM has stored any codes, the sequence will begin with Code 12 (3 times) followed by a long pause and then begin to flash any codes stored. Once it has displayed the last trouble code stored, the system starts over with Code 12 and repeats itself.

EXAMPLE: FLASH, pause, FLASH, FLASH, pause, FLASH, pause, FLASH, FLASH, pause FLASH, pause, FLASH, FLASH -long pause- FLASH, FLASH FLASH, FLASH, pause, FLASH, FLASH, FLASH -long pause- FLASH, pause, FLASH, FLASH, pause FLASH, pause, FLASH, FLASH, pause FLASH, pause, FLASH, FLASH

This example is the showing Code 43

This sequence will repeat continuously until you shut off the ignition.

Diagnostic trouble codes may be cleared by disconnecting the battery ground cable for at least 20 seconds. Reconnect negative battery cable and recheck codes to confirm the repair. OBDI can also be reset with a scanner, or by removing both ECM B and 1 fuses for 20 seconds as well.

Code 12 – Diagnostic mode

Code 13 - Oxygen sensor circuit - Oxygen sensor voltage stays between 0.35 and 0.55 volts for 30 seconds when the TPS signal was above 0.55 volts. The engine had been running for at least 40 seconds with an engine temperature above 110? F.

Code 14 - Coolant temperature sensor or circuit/ high temperature indicated - Coolant temperature sensor signal indicates a temperature of over 284? F for 4 seconds after the engine had been running for at least 10 seconds.

Code 15 - Coolant temperature sensor or circuit/ low temperature indicated - Coolant temperature sensor signal indicates a temperature colder than -36? F for at least 4 seconds after the engine had been running for 2 seconds.

Code 16 – System voltage high - Charging system voltage was either below 9 volts or above 17 volts for 10 seconds.

Code 17 – Crank Signal Circuit - PCM did not detect any spark reference pulses within 240 fuel control reference pulses (80 crank revolutions) while engine was running below 1200 RPM.

Code 19 – Crankshaft Position Sensor or circuit

Code 21 – Throttle Position Sensor TPS or circuit voltage high - TPS voltage was above 0.8 volts for 5 seconds when engine was running and air flow was less than 15 gm /sec, or the TPS voltage was over 4.8 volts at any time.

Code 22 – Throttle Position Sensor TPS or circuit voltage low - TPS voltage was under 0.2 volts for 4 seconds when the ignition was on.

Code 23 – Intake Air Temperature (IAT) sensor circuit – low temperature indicated - Inlet air temperature sensor signal showed an air temperature of -29? F for 4 seconds.

Code 24 - Vehicle Speed sensor circuit - Vehicle speed sensor signal showed less than 3 MPH for 2 seconds when engine speed was greater than 3000 RPM and transmission has not been in park or neutral for more than 4 seconds. Or vehicle speed goes from above 18 MPH to 0 in less than 2 seconds without applying brake.

Code 25 – Intake Air Temperature (IAT) sensor or circuit – high temperature indicated - Inlet air temperature sensor signal showed an air temperature of over 218? F for 5 seconds when vehicle speed was greater than 35 MPH.

Code 26 - Quad-Driver sense voltage shows a low voltage when battery voltage should be present, or if the sense voltage shows battery voltage when a low voltage should be present for at least 5 seconds when the engine was running.

Code 27 - 2nd gear switch was closed or grounded for 10 seconds when vehicle was in 4th gear, or 2nd or 4th gear switch was open when engine was first started.

Code 28 - 3rd gear switch was closed or grounded for 10 seconds when vehicle was in 4th gear, or 3rd or 4th gear switch was open when engine was first started.

Code 29 - 4th gear switch was closed or grounded for 10 seconds when vehicle was in 4th gear, or 4th gear switch was open when engine was first started.

Code 31 - Park/Neutral Position (PNP) switch circuit - PRNDL indicates a gear other than park or neutral for 13 seconds for 3 consecutive startups when ignition was on, engine was off and vehicle speed was 0. Or the PRNDL status indicators (A, B, C, P) showed an incorrect combination of Lo and Hi for more than 10 seconds.

Code 32 - Exhaust Gas Recirculation (EGR) Circuit - EGR open command did not change the fuel mixture when the command was given during off idle operation. EGR opening should cause the mixture to be slightly richer because of the low oxygen content of exhaust gas.

Code 33 - MAP sensor signal voltage was too high (low vacuum) for 5 seconds when throttle opening was under 2%.

Code 34 - MAP sensor signal voltage low - MAP sensor signal voltage was too low (high vacuum) when engine speed was over 1200 RPM, or the throttle angle was above 21% when engine speed was over 1200 RPM.

Code 35 - Idle Air Control (IAC) System

Code 38 – Brake Switch

Code 41 – Camshaft Sensor Circuit

Code 42 – Bypass or Electronic Spark Timing circuit - The EST signal did not change when the ECM applied bypass voltage to the ignition module.

Code 43 – Knock Sensor Ciruit - Knock sensor signal was either above 3.5 volts or below 1.5 volts for at least 20 seconds.

Code 44 - Oxygen sensor or circuit – lean exhaust detected. - Oxygen sensor voltage was under 0.25 volts for up to 4 1/2 minutes of closed loop operation.

Code 45 - Oxygen sensor or circuit - rich exhaust detected. - Oxygen sensor voltage was over 0.750 volts for 2 minutes in closed loop operation with a throttle angle between 0.6 and 1.9 volts.

Code 46 – Power Steering Pressure Switch circuit

Code 47 - Momentary loss of power to Body Computer Module (BCM).

Code 48 – Misfire Diagnosis

Code 51 - MEM-CAL, PROM, or ECM Error (Faulty or Incorrect Calibration)

Code 52 – CALPAK or ECM problem

Code 53 – System over-voltage – ECM over 17.7 volts

Code 54 – Fuel Pump Circuit

Code 55 - ECM problem

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).

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.