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DTC P1599: A/C Pressure Sensor Volts Too Low: Testing

    NOTE: Ensure the A/C system is properly charged with refrigerant.
  1. Start the engine. With the DRBIII®, read the A/C Pressure Sensor voltage. Is the voltage below 0.6 volt? If yes, go to next step. If no, go to step  10.
  2. Turn the ignition off. Disconnect the A/C Pressure Sensor harness connector. Turn ignition on, engine not running. Measure the voltage of the 5-Volt Supply circuit in the A/C Pressure Sensor harness connector. Is the voltage between 4.5 and 5.2 volts? If yes, go to next step. If no, go to step  7.
  3. With the DRBIII®, monitor the A/C Pressure Sensor voltage. Is the voltage above 0.6 volt? If yes, replace the A/C Pressure Sensor. If no, go to next step.
  4. Turn the ignition off. Disconnect the PCM harness connectors. Measure the resistance of the A/C Pressure Sensor Signal circuit in the A/C Pressure Sensor harness connector to ground. Is the resistance below 100 ohms? If yes, repair the A/C Pressure Sensor Signal circuit for a short to ground. If no, go to next step.
  5. Measure the resistance between the A/C Pressure Sensor Signal circuit and the Sensor ground circuit in the A/C Pressure Sensor harness connector. Is the resistance below 100 ohms? If yes, repair the A/C Pressure Sensor Signal circuit for a short to the Sensor ground circuit. If no, go to next step.
  6. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
  7. Turn the ignition off. Ensure A/C Pressure Sensor is disconnected. Disconnect the PCM harness connectors. Measure the resistance of the 5-Volt Supply circuit in the A/C Pressure Sensor harness connector to ground. Is the resistance below 100 ohms? If yes, repair the 5-Volt Supply circuit for a short to ground. If no, go to next step.
  8. Measure the resistance of the 5-Volt Supply circuit between the A/C Pressure Sensor harness connector and the PCM harness connector. Is the resistance below 5.0 ohms? If yes, go to next step. If no, repair the 5-Volt Supply circuit for an open.
  9. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
    10. NOTE: Ensure the A/C refrigerant System is properly charged
    WARNING: When the engine is operating, do not stand in a direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing.
  10. The conditions that set the DTC are not present at this time. The following may help in identifying the intermittent condition. With the engine running at normal operating temperature, monitor the DRBIII® parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set. Review the DRBIII® Freeze Frame information. If possible, try to duplicate the conditions under which the DTC was set. Refer to any Technical Service Bulletins (TSB) that may apply. With the DRBIII® as a Dual Channel Lab Scope and the Miller Special Tool (6801), backprobe the A/C Pressure Sensor Signal circuit at the A/C Pressure Sensor connector and PCM connector. Start the engine and look for any differences in the two patterns. Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals. Were any of the above conditions present? If yes, repair as necessary. If no, test is complete.
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