1981 Chevrolet Chevette Scooter, Standard TransFACTORY OEM SERVICE PROCEDURE

Entering Diagnostic Mode

  1. Turn ignition on (engine off). "CHECK ENGINE" lamp should glow. Locate Assembly Line Data Link (ALDL) connector attached to ECM wiring harness under instrument panel. Insert spade lug terminal across terminals "D" ("TEST" lead) and "E" (Ground). See Fig 1.
    Fig 1: Exploded View of ALDL Connector
    G09339974Courtesy of GENERAL MOTORS COMPANY
  2. "CHECK ENGINE" lamp should flash code "12". Code "12" consists of "FLASH", pause, "FLASH", "FLASH" followed by a longer pause. Trouble code "12" will be repeated 2 more times, then if any trouble codes are stored in ECM memory, they will be displayed in same manner.
  3. Trouble codes will be displayed from lowest to highest numbered code (3 times each) and be repeated as long as the "TEST" terminal of ALDL connector is grounded.
    CAUTION: Inserting lug in terminals of ALDL connector grounds "TEST" terminal lead. Do not ground ALDL connector before ignition is turned on or engine is started.
ECM TROUBLE CODE IDENTIFICATION

Code Circuit Affected
12 No reference pulses to ECM.
13 Oxygen sensor circuit.
14 Shorted coolant sensor circuit.
15 Open coolant sensor circuit.
21 Throttle position sensor circuit.
23 Open or grounded M/C solenoid circuit.
24 Vehicle speed sensor circuit.
32 BARO sensor circuit low.
34 MAP or vacuum sensor circuit.
35 ISC switch circuit shorted.
42 EST by-pass circuit grounded.
44 Lean oxygen sensor indication.
44 & 55 At same time, faulty oxygen sensor circuit.
45 Rich oxygen sensor indication.
51 Faulty PROM or improper PROM installation.
52 & 53 Faulty ECM.
54 Shorted M/C solenoid or faulty ECM.
55 Grounded +8 volts, voltage reference, faulty oxygen sensor or ECM.
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.