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 FAQ: QUAD4 ENGINE CONTROL UNIT FAULT CODES (1993)

If you own a 1982 to 1995 GM car or truck, you just might be able to read your trouble codes without any special tools or a diagnostic scanner. If you have a connector like this under your dash, read on... (note: this connector may have a black plastic cover over it, so also look for a cover shaped like this.

gm-aldl (1)

figure 1

How To Check For Fault Codes

1. Ground terminals A and B (see diagram below) with the ignition "ON" and engine not running. The system will enter the diagnostic mode. In this mode, the computer will display a Code 12, three consecutive times, by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" or light. A Code 12 consists of one flash, a short pause, then two flashes in rapid succession.

2. After Code 12 is displayed, any stored trouble codes will be displayed by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" light. All codes are displayed 3 times each then a code 12 will repeat. In the diagnostic mode, the computer will also energize all computer controlled relays and solenoids.

gm-aldl-connector

figure 2

These are the GM 2 Digit codes for 82 and up (non OBD-II) automobiles.

    code - code definition

  • 12- diagnostic mode (ECU typically flashes this twice before flashing fault codes. If the ECU continously flashes this code, it may mean there are no fault codes stored.)
  • 13- 02 sensor or circuit. <MORE INFO>
  • 14- coolant sensor or circuit/ high temp indicated. <MORE INFO>
  • 15- coolant sensor or circuit/ low temp indicated. <MORE INFO>
  • 16- system voltage out of range.  <MORE INFO>
  • 19- crankshaft position sensor or circuit
  • 21- throttle position sensor or circuit- voltage high <MORE INFO>
  • 22- throttle position sensor or circuit- voltage low <MORE INFO>
  • 23- mixture control (m/c) solenoid or circuit (carbureted models)
  • 23- manifold air temperature (mat) sensor or circuit (1990 and earlier models)
  • 23- intake air temperature (iat) sensor circuit (fuel-injected models) <MORE INFO>
  • 24- vehicle speed sensor (vss) or circuit  <MORE INFO>
  • 25- manifold air temperature (mat) sensor or circuit - high temperature indicated (1990 and earlier models)
  • 25- intake air temperature (iat) sensor or circuit - low temperature indicated (1991 and later models)  <MORE INFO>
  • 26- quad driver module circuit <MORE INFO>
  • 27- quad driver module circuit <MORE INFO>
  • 28- quad driver module circuit <MORE INFO>
  • 29- quad driver module circuit <MORE INFO>
  • 31- park/neutral position (pnp) switch circuit <MORE INFO>
  • 32- baro sensor or circuit (carbureted models)  <MORE INFO>
  • 32- egr circuit (fuel-injected models) <MORE INFO>
  • 33- manifold absolute pressure (map sensor signal voltage high  <MORE INFO>
  • 33- mass air flow (maf) sensor or circuit - excessive airflow indicated
  • 34- manifold absolute pressure (map) sensor signal voltage low  <MORE INFO>
  • 34- mass air flow (maf) sensor signal - low airflow indicated
  • 35- idle speed control (isc) switch or circuit (shorted) (carbureted models)
  • 35- idle air control (iac) valve/ circuit  <MORE INFO>
  • 38- brake switch circuit <MORE INFO>
  • 39- torque converter clutch (tcc) or clutch switch circuit <MORE INFO>
  • 41- no distributor signals to ecm, or faulty ignition module ( carbed models) <MORE INFO>
  • 41- cylinders select error- mem-cal or ecm problem ( fuel-injected models) <MORE INFO>
  • 41- cam sensor circuit (3.8 engine) <MORE INFO>
  • 42- bypass or electronic spark timing (est) circuit <MORE INFO>
  • 43- low voltage at ecm terminal l (carbureted models) <MORE INFO>
  • 43- knock sensor circuit <MORE INFO>
  • 44- oxygen sensor or circuit - lean exhaust detected <MORE INFO>
  • 45- oxygen sensor or circuit - rich exhaust detected <MORE INFO>
  • 46- power steering pressure switch circuit <MORE INFO>
  • 48- misfire diagnosis  <MORE INFO>
  • 51- prom, mem-cal or ecm problem <MORE INFO>
  • 52- calpak or ecm problem  <MORE INFO>
  • 53- egr fault (carbureted models only)
  • 53- system over-voltage (ecm over 17.7 volts) <MORE INFO>
  • 54- mixture control (m/c) solenoid or circuit (carbureted models)
  • 54- fuel pump circuit (1986 and later models) <MORE INFO>
  • 55- oxygen sensor circuit or ecm <MORE INFO>
  • 61- oxygen sensor signal faulty (possible contaminated sensor)
  • 62- transaxle gear switch signal circuits
  • 63- manifold absolute pressure (map) sensor voltage high (low vacuum detected) <MORE INFO>
  • 64- manifold absolute pressure (map) sensor voltage low (high vacuum detected) <MORE INFO>
  • 66- pressure sensor or circuit air conditioning  <MORE INFO>

 


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