Powertrain Controls - ECM/PCM

DTC 61 Chart:

A/C Circuit:

Circuit Description:
A/C refrigerant charge is calculated by the inputs from the A/C refrigerant pressure and A/C evaporator temperature sensors. The PCM will calculate system charge when the A/C is selected "ON" by using three variables. A/C evaporator temperature, A/C refrigerant pressure and vehicle speed are factored together to yield a minimum charge allowable for the A/C system to operate. As ambient temperature falls, so does static (A/C "OFF") refrigerant pressure. This produces a sliding scale which requires temperature, pressure and vehicle speed inputs to calculate a reliable system charge value that indicates when A/C refrigerant charge is too low to safely allow the compressor to operate.

DTC 61 Will Set When:
The system charge falls below a given value for the temperature and vehicle speed variables or if the status line is intermittently "OPEN" or grounded.

Action Taken (PCM will default to):
The MIL will not become illuminated, the A/C compressor will be disabled, the cooling fan will not be enabled unless A/C had been requested first and the vehicle speed is above 35 mph with a current DTC 61.

DTC 61 Will Clear When:
A current DTC 61 will clear when A/C charge falls within the calibrated threshold. A history DTC 61 will clear after 50 consecutive ignition key cycles without a current DTC 61 being stored.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test determines if DTC is intermittent and will also check the A/C system for other failures. Repair all other DTC(s) first before proceeding.

2. This test is to evaluate the A/C refrigerant pressure sensor for accuracy. A reliable gage set should be used and no more than 20 psi difference in pressure between gages and Tech 1 is allowable.

3. The system is operating though DTC 61 is intermittent.

Diagnostic Aids:
After a subsequent key cycle, the A/C will be enabled and DTC 61 will be erased from the current DTC memory and added as a history DTC. If A/C pressure, evaporator temperature and vehicle speed again indicate a low charge, the PCM will store a current DTC 61 and disable the A/C compressor clutch. Only after a relatively high number of failures occur will the A/C be disabled and become inoperative until the code is cleared, from both current and history DTC memory.

The A/C status circuit allows the PCM to determine if the clutch is receiving a complete circuit via the A/C relay. If the status line is intermittently open or grounded a DTC 61 may set.