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Home › Chevrolet › 1988 › Spectrum Express › Repair and Diagnosis › Engine Performance › System › 1.5L EFI Turbo › Trouble Shooting › Component Testing By Trouble Code › Code 42 (Electronic Spark Timing)

Code 42 (Electronic Spark Timing)

  1. Clear code. Turn ignition off. Disconnect ECM harness connectors. Turn ignition on. Using an ohmmeter, probe harness connector terminal B20 to ground. Reading should be less than 500 ohms.
  2. If resistance test is not proper, check circuit B20 for open. If circuit B20 has continuity, check connectors for poor connections. If connections are good, replace ECM.
  3. If resistance reading in step 1) was proper, probe ECM harness connector terminal B21 with a test light connected to 12 volts. If test light comes on, go to step 6)
  4. If test light does not light, connect an ohmmeter between ECM harness connector B20 and ground. Probe harness connector B21 with test light connected to 12 volts. Ohmmeter reading should change from less than 500 ohms to over 5000 ohms when B21 is probed.
  5. If resistance does not change, disconnect distributor 4 way connector. Ohmmeter should indicate an open circuit (high reading). If open circuit is not indicated, repair circuit B20. If open circuit is indicated, check circuit B21 for open, poor connection at distributor or bad ECM.
  6. If test light came on in step 3), disconnect distributor 4-way connector. If test light is still on, circuit B21 is shorted to ground.
  7. If test light goes off in step 6), check for short to ground between 4-way connector and Green/White wire ignition module terminal. If no short is present, replace ignition module.
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