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Home >> Saturn >> 2002 >> L200 Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> System Tests >> 5-Volt Reference Circuit Error Diagnosis >> Diagnostic Procedures
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Diagnostic Procedures

  1. Turn ignition on, engine off. Using scan tool, monitor A/C HIGH SIDE PRESS. SENSOR, FUEL TANK PRESS. SENSOR and TP SENSOR. If all 3 readings are less than 0.2 volt, go to next step. If all 3 readings are not less than 0.2 volt, go to step  4 .
  2. Disconnect one sensor at a time while using scan tool to monitor voltage of another sensor on 5-volt reference line. When only one sensor is left connected, reconnect a sensor that was previously disconnected and disconnect last sensor that was not tested. If voltage on monitored sensor changes to a normal reading when any one component is disconnected, replace disconnected component. If voltage on monitored sensor does not change to a normal reading when any one component is disconnected, go to next step.
  3. Five-volt reference is shorted to ground or PCM is faulty. To locate short to ground, turn ignition off and disconnect PCM connectors J1 and J2. Check continuity between Gray wire and ground and between Gray wire and Black wire at each sensor connector. If continuity exists on any circuit, repair short to ground in that circuit. If continuity does not exist on any circuit, replace PCM.
  4. Press accelerator to wide open throttle. Using scan tool, monitor A/C HIGH SIDE PRESS. SENSOR, FUEL TANK PRESS. SENSOR and TP SENSOR. If A/C HIGH PRESS. SENSOR is more than 4 volts, and FUEL TANK PRESS. SENSOR and TP SENSOR are at 5 volts, go to next step. If A/C HIGH PRESS. SENSOR is not more than 4 volts, and FUEL TANK PRESS. SENSOR and TP SENSOR are not at 5 volts, problem is intermittent. See DIAGNOSTIC AIDS  .
  5. Disconnect A/C pressure sensor, fuel tank pressure sensor and TP sensor. Using DVOM, measure voltage on Gray wire at TP sensor connector. If voltage is more than 6 volts, go to next step. If voltage is less than 6 volts, A/C HIGH SIDE PRESS. SENSOR is more than 4 volts, and FUEL TANK PRESS. SENSOR and TP SENSOR are 5 volts on scan tool (accelerator pedal at wide open throttle), replace PCM.
  6. Five-volt reference is shorted to voltage. To locate short to voltage, turn ignition on, connect DVOM between Gray wire and ground. Pull each fuse in underhood fuse block while monitoring DVOM for change in voltage. Do not pull PCM fuse (CONTROLS B+, IGN 0 or CONTROLS IGN 1) at this time. If voltage drops to 4-6 volts when a fuse is pulled, a short to that circuit exists. See appropriate POWER DISTRIBUTION article IN WIRING DIAGRAMS to locate and repair short in circuit. If voltage does not drop to 4-6 volts when a fuse is pulled, go to next step.
  7. Turn ignition off. Disconnect PCM connectors J1 and J2. Turn ignition on, engine off. If voltage does not drop to zero volts, 5-volt reference is shorted a PCM voltage supply circuit. See appropriate POWER DISTRIBUTION article IN WIRING DIAGRAMS. Repair as necessary. If voltage drops to zero volts, 5-volt reference is shorted to another PCM voltage source. Check continuity between 5-volt reference circuit and all other PCM circuits. Repair circuits where continuity exists as necessary.
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