To retrieve information from the ECM (electronic control module). You can use a scan tool, or a code reader. I have seen code readers for sale for $18cdn. Or you can use a small piece of wire and connect pin A and pin B in the Assembly Data Link Connector (ALDL). The ALDL is located under your steering column near the center console.
Turn of your ignition, then Ground the ECM (by connecting pin A and B). Turn your key on but don’t start your vehicle. Have a pen and paper ready as the engine light with give you code 12, indicated by 1 flash, a pause, and then 2 flashes. The code will be flashed three times, after that it will indicate stored trouble codes, Each Code is Flashed Three Times!!. When all codes have been identified code 12 will flash. If code 12 flashes non stop then the ECM has no codes.
If you have an intermittent code the engine light will come on but only remain on for 10 seconds.
To clear codes from your ECM remove your negative terminal for a minimum of 10 seconds.
| Trouble Codes |
Circuit or System |
Probable Cause |
| 12 |
No distributor reference pulses to ECM |
This code will flash whenever the diagnostic terminal is grounded with
the ignition turned on and the engine not running. If additional codes are
stored in the ECM they will appear after this code has flashed three times.
If this code appears while the engine is running, no reference pulses from
the distributor are reaching the ECM. |
| 13 |
Oxygen sensor circuit |
Check for sticking or misadjusted throttle position sensor. Check the
wiring and connectors from the oxygen sensor. Replace teh oxygen sensor. |
| 14 |
Coolant sensor/high temp |
If the engine is experiencing overheating problems the problem must be
rectified before continuing. Check all wiring and connections associated
with the coolant temperature sensor. Replace the coolant temperature sensor.
* |
| 15 |
Colant sensor/low temp |
See above then check the wiring connections at the ECM. |
| 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. |
| 22 |
Throttle position sensor/voltage low |
Check the TPS adjustment. Check the ECM connector. Replace the TPS. |
| 23 (Carbureted) |
Mixture control solenoid |
The mixture control solenoid is open or grounded. |
| 23(fuel-injected) |
MAT low temp indication |
Sets if the manifold air temperature sensor, connections or wires are
open for 3 seconds. |
| 23 (1992 CPI only) |
IAT low temp indication |
Sets if the manifold air temperature sensor, connections or wires are
open for 3 seconds. |
| 24 |
Vehicle speed sensor |
A fault in this circuit should be indicated only when the vehicle is in
motion. Disregard Code 24 if it is set when the drive wheels are not
turning. Check the connections at the ECM. Check the TPS setting. |
| 25 |
ATI sensor/high air |
High temperature indication. Sets if the sensor or signal line becomes
grounded for 3 seconds. |
| 32(Carbureted) |
BARO circuit low |
Barometric pressure sensor circuit low. |
| 32 (Fuel-injected) |
EGR |
Vacuum switch shorted 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 specified period of time. Replace the EGR valve. * |
| 33 |
MAP sensor |
Check the vacuum hose from the MAP sensor. Check the electrical
connections at the ECM. Replace the MAP sensor. * |
| 34 |
Vacuum sensor or MAP sensor |
Code 34 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.* |
| 35 (Carbureted) |
ISC vavle |
Idle speed control error. Replace the ISC.* |
| 35 (Fuel-injected) |
IAC valve |
Idle air control error. Code will set when colsed throttle speed is 50
rpm above or below the correct idle speed for 30 seconds. Replace the IAC. * |
| 42 |
Electronic Spark Timing (EST) |
Electronic Spark Timing bypass circuit or EST circuit is grounded or
open. A malfunctioning HEI module can cause this code. |
| 43 |
Electronic Spark Control |
The ESC retard signal has been on for too long or the system has (ESC)
unit failed a function check. |
| 44 |
O2 sensor indicates lean |
Check the ECM wiring connections, particularly terminals 15 and 8.
Exhaust. Check for vacuum leakage at the TBI base gasket, vacuum hoese or
the intake manifold gasket. Replace the oxygen sensor. * |
| 45 |
O2 sensor indicates rich |
Check the evaporative charcoal canister and its components for the
exhaust presence of fuel. Replace the oxygen sensor. |
| 51 |
PROM or MEM-CAL |
Make sure that the PROM or MEM-CAL is properly installed in the ECM.
Replace the PROM or MEM-CAL. |
| 52 |
CALPAK |
Check the CALPAK to insure proper installation. Replace the CALPAK/ * |
| 53 |
System over-voltage (indicates a basic alternator problem) |
Check the charging system. |
| 54 (Fuel-injected) |
Fuel pump |
Low fuel pump voltage. Sets when the fuel pump voltage is less than 2
volts when reference pulses are being received. |
| 54 (Carbureted) |
M/C solenoid |
Check all M/C solenoid and ECM wires and connections. *Replace if
necessary with a new unit. |
| 55 |
ECM |
Be sure that the ECM ground connections are tight. If they are, replace
the ECM.* |
| *Component replacement may not cure the problem in all
cases. For this reason, you may want to seek professional advice before
purchasing replacement parts. |
