MTC 74

74 - AC REQUEST OUTPUT SIGNAL TOO LOW (MTC)

74 - AC Request Output Signal Too Low (MTC):

WHEN MONITORED
With the ignition on.

SET CONDITION
If the A/C Heater Control detects voltage below 1.51 volts on the (C221) A/C Switch Sense circuit.

POSSIBLE CAUSES
- (C221) A/C switch sense circuit shorted to ground
- (C221) A/C switch sense circuit open
- Instrument cluster (CCN)
- A/C heater control

NOTE: This DTC must be active for the results of this test to be valid. Do not perform this test if this DTC is stored. Refer to HVAC System Test (MTC) for stored DTC test procedures.

Diagnostic Test




1. CHECK (C221) A/C SWITCH SENSE CIRCUIT VOLTAGE AT A/C HEATER CONTROL C1 HARNESS CONNECTOR

Turn the ignition off.
Disconnect the A/C Heater Control C1 harness connector.
Turn the ignition on.
Measure the voltage of the (C221) A/C Switch Sense circuit.

Q: Is the voltage below 4.8 volts?

YES: Go To 2
NO: Replace the A/C Heater Control. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test




2. CHECK (C221) A/C SWITCH SENSE CIRCUIT FOR A SHORT TO GROUND

Turn the ignition off.
Disconnect the Instrument Cluster C3 harness connector.
Measure the resistance of the (C221) A/C Switch Sense circuit between ground and the A/C Heater Control C1 harness connector.

Q: Is the resistance below 10K ohms?

YES: Repair the (C221) A/C Switch Sense circuit for a short to ground. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 3




3. CHECK (C221) A/C SWITCH SENSE CIRCUIT FOR AN OPEN

Measure the resistance of the (C221) A/C Switch Sense circuit between the A/C Heater Control C1 harness connector and the Instrument Cluster C3 harness connector.

Q: Is the resistance below 5.0 ohms?

YES: Replace the Instrument Cluster (CCN). Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Repair the (C221) A/C Switch Sense circuit for an open. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test