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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 85 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 2.2L)DIAGNOSTIC TESTSDTC P0530: A/C REFRIGERANT PRESSURE SENSOR CIRCUITDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedures

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: If DTC P1635 is also set, diagnose that DTC first. See DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT  .
  1. Turn ignition on, with engine off. Using scan tool, monitor A/C high side pressure. If scan tool reading is less than 0.2 volt, go to next step. If scan tool reading is 0.2-3.8 volts, problem is intermittent. See DIAGNOSTIC AIDS  . If scan tool reading is more than 3.8 volts, go to step  8 .
  2. Disconnect A/C pressure sensor harness connector located in right front corner of engine compartment. Using a jumper wire, connect jumper between A/C pressure sensor harness connector terminals No. 2 (Gray wire) and No. 3 (Red/Black wire). If scan tool reading is not more than 3.8 volts, go to next step. If scan tool reading is more than 3.8 volts, check for loose connection. Repair as necessary. If terminals are okay, replace A/C pressure sensor.
  3. Remove jumper wire. Using a DVOM, check voltage between ground and A/C pressure sensor harness connector terminal No. 2 (Gray wire). If voltage reading is 4-6 volts, go to step  5 . If voltage reading is not 4-6 volts, go to next step.
  4. Using scan tool, monitor FUEL TANK PRESS. SENSOR. If reading is not less than 0.2 volt, check Gray wire for open. If Gray wire is okay, replace ECM. If reading is less than 0.2 volt, 5-volt reference shorted to ground or ECM error. See DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT  .
  5. Turn ignition off. Disconnect ECM harness connector J1. Check for continuity in Red/Black wire between ECM and A/C pressure sensor. If continuity does not exist, repair open in circuit. If continuity exists, go to next step.
  6. Check for continuity between ground and A/C pressure sensor harness connector terminal No. 3 (Red/Black wire). If continuity exists, repair short to ground in Red/Black wire. If continuity does not exist, go to next step.
  7. Check for short between harness connector terminals No. 1 (Black wire) and No. 3 (Red/Black wire) circuits. Repair as necessary. If circuits are okay, check for loose connection at harness connectors. Repair as necessary. If terminals are okay, replace ECM.
  8. Disconnect A/C pressure sensor harness connector. Check scan tool reading. If scan tool reading is less than 0.2 volt, go to next step. If scan tool reading is not less than 0.2 volt, go to step  10 .
  9. Using a DVOM, check voltage between A/C pressure sensor harness connector terminals No. 1 (Black wire) and No. 2 (Gray wire). If voltage reading is 4-6 volts, replace pressure sensor. If voltage reading is not 4-6 volts, check for open in Black wire circuit. Repair as necessary. If circuit is okay, check for loose connection at harness connectors. Repair as necessary. If terminals are okay, replace ECM.
  10. Turn ignition off. Disconnect ECM harness connector J1. Turn ignition on. Using DVOM, check for voltage at A/C pressure sensor harness connector terminal No. 3 (Red/Black wire). If voltage is present, repair short to voltage in circuit. If voltage is not present, check A/C pressure sensor harness connector terminals No. 2 (Gray wire) and No. 3 (Red/Black wire) circuits for short to each other. Repair as necessary. If circuit is okay, replace ECM.
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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.