Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC P2518 11: A/C Refrigerant Low Side Fluid Pressure Sensor Circuit Above Maximum ThresholdDTC P2518 12: A/C Refrigerant Low Side Fluid Pressure Sensor Circuit Below Minimum Threshold
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
5-Volt Reference | P2518 12 | P2518 12 | -- | -- |
A/C Refrigerant Pressure Sensor Signal | P2518 12 | P2518 12 | P2518 11 | -- |
Low Reference | -- | P2518 11 | -- | -- |
Circuit/System Description
The HVAC control module monitors the low side refrigerant pressure through the A/C refrigerant pressure sensor. The HVAC control module supplies a 5-volt reference and a low reference to the sensor. Changes in the A/C refrigerant pressure cause the sensor signal to the HVAC control module to vary. When the pressure is high, the signal voltage is high. When the pressure is low, the signal voltage is low. When pressure is high, the HVAC control module sends a message to the ECM to turn on the cooling fans on. When pressure is too high or too low, the HVAC control module will not allow the A/C compressor to operate.
Conditions for Running the DTC
| • | Engine is running. |
| • | Any of the conditions for setting the DTC are met for 15 seconds. |
Conditions for Setting the DTC
| • | The HVAC control module detects that the A/C pressure is less than 2.03 psi (14 kPa) sets DTC P2518 12. |
| • | The HVAC control module detects that the A/C pressure is more than 101.5 psi (700 kPa) sets DTC P2518 11. |
Action Taken When the DTC Sets
The A/C compressor is disabled.
Conditions for Clearing the DTC
| • | The history DTC will clear after 40 consecutive ignition cycles have occurred without a malfunction. |
| • | The DTC will become history if the HVAC control module no longer detects a failure. |
Diagnostic Aids
A malfunction within the refrigerant system causing high pressure can cause this DTC to set.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Ignition ON, observe the scan tool Low Pressure Switch parameter. The parameter should read closed.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the A/C refrigerant pressure sensor.
- Ignition OFF, test for less than 10 ohms between the low reference circuit terminal 1 and ground.
- Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 2 and ground.
- Verify the scan tool Low Pressure Switch parameter is Open.
- Install a 3A fused jumper wire between the signal circuit terminal 3 and the 5-volt reference circuit terminal 2. Verify the scan tool Low Pressure Switch parameter is Open.
- If all circuits test normal, test or replace the A/C refrigerant pressure sensor.
| ⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. |
| ⇒ | If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. |
| ⇒ | If greater than the specified range, test the 5-volt reference circuit for a short to voltage. |
| ⇒ | If not the specified value, test the signal circuit terminal 3 for a short to voltage. |
| ⇒ | If not the specified value, test the signal circuit for short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for the HVAC control module replacement, setup, and programming |
