Powertrain Controls - ECM/PCM

DTC 61 Chart A/C System Performance:

A/C System Wiring Diagram:

Circuit Description:

A/C refrigerant charge is calculated by the inputs from the A/C refrigerant pressure and A/C evaporator temperature sensors. The ECM 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.

If system charge falls below a given value for the temperature and vehicle speed variables, a DTC 61 will set. 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.

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 scan tool is allowable.

3. The system is operating though DTC 61 is intermittent. Hardware failures including worn compressor etc should be diagnosed.

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 ECM 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.

A/C status circuit allows the ECM 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.