When the driver turns on the Air Conditioning a signal is sent to the ECM. When the ECM has all conditions set and is ready to engage the compressure, it activate the A/C clutch relay. To activate the relay, the ECM completes the relay coil ground circuit. The ECM delays grounding the relay circuit for a short time, so the ECM can adjust the engine idle speed for the additional load. The ECM will temporarily de-energized the A/C clutch relay for one or more of the following conditions:
-Full acceleration when the throttle is at WOT.(Wide Open Throttle)
-Risk of overheating: Engine coolant temp. exceeds threshold value
-A/C system pressure exceeds threshold value
-Engine starting
ECM monitors inputted voltage through A/C compressor relay. Checking voltage every 10 sec. under detecting condition, if the voltage lower than the specified value is detected for more than 5 sec., ECM sets P0646.
Item | Detecting Condition | Possible cause |
DTC Strategy |
•
Detects circuit short to low voltage |
•
Poor connection
•
Open or short to ground in A/C relay circuit
•
Faulty ECM |
Enable Conditions |
•
After 0.5 sec under conditions below
•
No DTC exists
•
Engine works
•
11V ≤ Battery voltage ≤ 16V | |
Threshold value |
•
Open or short to ground | |
Diagnosis Time |
•
Continuous (More than 5 seconds failure for every 10 seconds test) | |
MIL On Condition |
•
DTC only (NO MIL ON) |
Coil Resistance | 70Ω ~ 120Ω |
