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Home >> Cadillac >> 1983 >> Eldorado 5.7 N >> Repair and Diagnosis >> Engine Performance >> System >> DFI Tests W/Codes >> Diagnostic Code Charts >> Code 20 - Open Fuel Pump Circuit >> Diagnostic Aids
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Diagnostic Aids

NOTE: The following procedure is designed to account for intermittent codes. If no malfunction is uncovered using this procedure, it will indicate that the DFI system is OK at this time. Refer to NOTE ON INTERMITTENTS if further investigation is necessary.

When the ignition is turned on, the ECM energizes the fuel pump relay for 2 seconds which feeds 12 volts to the fuel pump (circuit 120). As soon as distributor reference pulses are received, the ECM energizes the fuel pump relay so that the fuel pump circuit is fed 12 volts while the engine 15 running.

Trouble Code 20 indicates that the fuel pump relay circuit did not supply 12 volts to the fuel pump. Possible causes of this condition are:

  1. To determine if the Code 20 is hard or intermittent turn the ignition off for 10 seconds to power down the ECM. Turn the ignition on for 5 seconds and then attempt to start the engine. If the engine now starts but Code 20 is not stored hard, then the malfunction is not present at this time. If the engine will not start, check the fuel pump fuse. If the engine starts with a hard Code 20 stored, it must then be determined if the ECM is receiving the proper feedback signal. If the "battery voltage" (parameter .1.0) reads 0 volts then check circuit 120 leading to the ECM for an open. If circuit 120 is OK, check for a faulty ECM connector or faulty ECM.
  2. If the engine wil1 not run and the fuel pump is OK, or if the engine starts and parameter .1.0 reads battery voltage, the next step is to verify if the ECM is supplying a signal to the fuel pump relay. If the test light on circuit 465 does not light, reinstall the fuel pump relay and then check the circuit for an open or short to ground. If circuit 465 is OK, check for a faulty ECM connector or faulty ECM. If a short to ground is discovered, it must be repaired and then circuit 465 should again be checked for the proper signal. The short to ground could have damaged the ECM.
  3. If the test light on circuit 465 does light for 2 seconds then the ECM is supplying the proper signal to energize the fuel pump relay. If the test light on circuit 120F does not light, an open must exist in circuits 120F or 3.
  4. If the test light on circuit 120F does light, then the fuel pump relay is receiving 12 volts. Now determine if the relay is receiving a good ground from the ECM through circuit 497. If the test light between circuits 120F and 497 will not light with ignition on, then check circuit 497 for an open between the ECM and the relay. If circuit 497 is OK, check for a faulty ECM connector or faulty ECM.
  5. If the test light does light, then we have a good ground. Check for continuity in circuit 120E. If the test light between circuits, 120F and 120E will not light with ignition on, then circuit 120E must be repaired for an open. If the test lights, then the fuel pump relay is failing to close and should be replaced.
  6. If the fuel pump fuse is blown, it will be necessary to determine the cause of the excessive current draw. Battery voltage parameter .1.0 of the engine data series uses the fuel pump feedback signal as its source of voltage. With voltage applied to circuit 120E through the test light, a 0 voltage reading on the diagnostic display would indicate a short to ground in the system. If the display reads 0 volt, disconnect the 6-way weatherpack connector at the fuel tank and note the parameter value.
  7. If the display reads 0 a short stil1 exists. If a voltage is displayed after removing the oil pressure switch connector, the switch must be shorted and should be replaced. If it remains at a 0 volt reading, the short is in either circuit 120 or 120E.
  8. If the display now reads more than 0 volt, check the wiring between the 6-way weatherpack connector and the fuel pump for a short to ground. If the wiring is OK, the fuel pump must be inspected for a short to ground.
  9. If the display of parameter .1.0 did not read 0 volt at the beginning of the procedure, then the short to ground is either in the fuel pump relay, the oil pressure switch or the wiring harness. If the test light on circuit 120F does not light, the fuel pump relay must be shorting to ground and should be replaced. If the test light does light, the short still exists. If the light goes out after removing the oil pressure switch connector the switch is shorted and should be replaced. If the test light does light, the short to ground is in circuit 120F.
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