Circuit Description
The PCM monitors A/C refrigerant pressure and A/C evaporator temperature to determine if the A/C system has adequate refrigerant (R134a) charge. The PCM will disable the A/C clutch whenever A/C refrigerant charge drops below a predetermined value, to reduce the chance of compressor damage. The PCM will cycle the compressor more frequently if the charge is slightly low. The PCM determines A/C charge based on A/C refrigerant pressure and A/C evaporator temperature. The PCM uses these two inputs to calculate A/C refrigerant charge.
Conditions for Setting the DTC
The PCM calculates refrigerant charge to be below a predetermined level.
Action Taken When the DTC Sets
| • | DTC P1543 will be stored in the PCM memory when the diagnostic runs and fails. |
| • | The Malfunction Indicator Lamp (MIL) will not illuminate. |
| • | A/C efficiency will decrease or A/C operation will be completely disabled. |
| • | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in Failure Records. |
Conditions for Clearing the MIL/DTC
| • | If no failures are reported by this or any other non-emission related diagnostic. |
| • | A last test failed (Current DTC) will clear when the diagnostic runs and does not fail. |
| • | PCM battery voltage is interrupted. |
| • | Using a Scan tool. |
Diagnostic Aids
An A/C evaporator temperature sensor and/or an A/C refrigerant pressure sensor that is slewed (shifted in value) could cause a DTC P1543.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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Underhood temperature should be above 16°C (60°F), before proceeding.
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The A/C performance test must be performed. A/C system hardware (A/C compressor, thermal expansion valve etc.) could cause a DTC P1543 to set.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 | Install the A/C manifold gauge set (Refer to Section 1B). Is the A/C refrigerant pressure (low side) greater than the specified value? | 45 psi | Go to Section 1B1 for further A/C system diagnosis | |
3 |
Do the two readings agree within the specified range? | ±10 psi | ||
4 |
Does DTC P0531 set? | -- | Go to DTC P0531 Air Conditioning (A/C) Refrigerant Pressure Sensor Performance | |
5 | Does the A/C compressor clutch engage? | -- | Go to Section 1B1 for further A/C system diagnosis | Go to Air Conditioning (A/C) Request Circuit Check for further A/C system diagnosis. |
6 |
Is the test light ON? | -- | ||
7 | Check the connection at the A/C refrigerant pressure sensor. Was a problem found? | -- | ||
8 | Replace the A/C refrigerant pressure sensor. Is the action complete? | -- | System OK | -- |
9 | Repair connector. Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Is the action complete? | -- | System OK | -- |
10 | Repair open in the A/C refrigerant pressure sensor ground circuit.Refer to Repair Procedures in Electrical Diagnosis (8A Cell 5). Is the action complete? | -- | System OK | -- |
