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Home >> Saturn >> 1997 >> SW2 Automatic >> Repair and Diagnosis (Single Page) >> Engine Performance >> Testing & Diagnosis >> Engine Controls - Self-Diagnostics >> Diagnostic Trouble Codes >> DTC P0506, P0507, P1508 &/Or P1509 - Rpm Out Of Range &/Or IAC Valve Circuit Fault >> Diagnostic Procedures

Diagnostic Procedures

  1. Warm engine to normal operating temperature (greater than 176°F). Install scan tool. Using scan tool, extend and retract IAC pintle while observing RPM change. If RPM changes, go to next step. If RPM does not change, go to step 4).
  2. Exit scan tool control. Monitor actual RPM and desired RPM. If actual RPM is within 100 RPM of desired RPM, problem is intermittent. See DIAGNOSTIC AIDS. If actual RPM is not within 100 RPM of desired RPM, go to next step.
  3. If idle is too high, use scan tool to determine RPM is at idle command. If not at idle command, check TP sensor throttle linkage including cruise control adjustment (if equipped). If linkages are okay, check for vacuum leak. If idle is too low, check accessory drive components or causes of unstable/rough running.
  4. Turn ignition on. Disconnect IAC valve. Turn ignition on. Using scan tool, cycle valve from open to closed using the position control feature of the scan tool. While commanding motor position open and closed, probe each IAC connector pin with a test light connected to ground, then test again with test light connected to battery voltage. Go to next step.
  5. With test light connected to ground, test light should blink when connected to IAC terminals "A" and "C", then turn off. With test light connected to battery voltage, test light should blink and then stay on steady. With test light connected to ground, test light should blink and then stay on steady when connected to IAC terminals "B" and "D". With test light connected to battery voltage, test light should blink and then turn off. If all 4 circuits tested properly, go to next step. If not all 4 circuits tested properly, go to step 7).
  6. Check for terminal tightness at harness connectors. If terminals are okay, check for faulty IAC valve.
  7. If test light stayed on steady when it should be off, check for shorted circuit to battery voltage. Repair as necessary. If circuit is okay, go to next step. If test light does not turn on when it should be on, check circuits for open or shorted to ground. Repair as necessary. If circuits are okay, go to next step.
  8. If all circuits are okay, disconnect PCM harness connector J2. Check resistance between all possible combinations of 2 circuits (i.e. terminals "A" to "B" or terminals "C" to "D"). If resistance reading is less than 2 ohms (open circuit), repair circuits shorted together. If resistance is 2 ohms or greater, check terminal tightness to harness connectors. If terminals are okay, replace faulty PCM.
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