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MTC 33

33-A/C MODE SWITCH STUCK (MTC)


33 - A/C Mode Switch Stuck (MTC):





Theory of Operation
The A/C mode switch input changes when the switch is pushed down. A stored DTC 33 indicates that the A/C mode switch was stuck in a pushed position for more than 10 minutes, but has since returned to its normal state. An active DTC 33 indicates that the A/C mode switch is stuck in a pushed position. An active DTC 33 will prevent the control from entering diagnostic mode and performing certain diagnostic functions. It will also prevent proper A/C mode switch and status indicator function.

WHEN MONITORED
With the ignition on.

SET CONDITION
If the A/C mode switch stays in a pushed position for more than 10 minutes.

POSSIBLE CAUSES
- Object holding A/C mode switch in a pushed position
- Substance causing A/C mode switch to get stuck in a pushed position
- (C850) Blower switch position signal circuit shorted to voltage
- (C850) Blower switch position signal circuit shorted to (Z908) ground circuit
- (C850) Blower switch position signal circuit shorted to (Z909) ground circuit
- (C850) Blower switch position signal circuit shorted to ground
- (C850) Blower switch position signal circuit open
- A/C Status indicator inoperative
- A/C Heater control

DIAGNOSTIC TEST

1. INSPECT THE A/C HEATER CONTROL FOR DAMAGE
Turn the ignition off.
Inspect the A/C Heater Control for damage.

Q: Is the A/C Heater Control damaged?

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

2. INSPECT FOR OBJECT OR SUBSTANCE CAUSING THE A/C MODE SWITCH TO STAY OR STICK IN A PUSHED POSITION
Inspect the A/C Heater Control for anything that would cause the A/C mode switch to stay or stick in a pushed position.

Q: Is anything present that would cause the A/C mode switch to stay or stick in a pushed position?

YES: Repair as necessary.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 3

3. CHECK THE (C850) BLOWER SWITCH POSITION SIGNAL CIRCUIT VOLTAGE




Disconnect the A/C Heater Control C3 harness connector.
Turn the ignition on.
Measure the voltage of the (C850) Blower Switch Position Signal circuit.

Q: What is the voltage?

Below 4.8 volts
Go To 4

Above 5.2 volts
Go To 8

4.8 volts To 5.2 volts
Go To 9

4. CHECK THE (C850) BLOWER SWITCH POSITION SIGNAL CIRCUIT FOR A SHORT TO THE (Z908) GROUND CIRCUIT




Turn the ignition off.
Measure the resistance between the (C850) Blower Switch Position Signal circuit and the (Z908) Ground circuit in the A/C Heater Control C3 harness connector.

Q: Is the resistance below 10K ohms?

YES: Repair the (C850) Blower Switch Position Signal circuit for a short to the (Z908) Ground circuit.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 5

5. CHECK THE (C850) BLOWER SWITCH POSITION SIGNAL CIRCUIT FOR A SHORT TO THE (Z909) GROUND CIRCUIT




Disconnect the A/C Heater Control C1 harness connector.
Measure the resistance between the (C850) Blower Switch Position Signal circuit and the (Z909) Ground circuit in the A/C Heater Control C1 harness connector.

Q; Is the resistance below 10K ohms?

YES: Repair the (C850) Blower Switch Position Signal circuit for a short to the (Z909) Ground circuit.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 6

6. CHECK THE (C850) BLOWER SWITCH POSITION SIGNAL CIRCUIT FOR A SHORT TO GROUND




Measure the resistance of the (C850) Blower Switch Position Signal circuit between ground and the A/C Heater Control C3 harness connector.

Q: Is the resistance below 10K ohms?

YES: Repair the (C850) Blower Switch Position Signal circuit for a short to ground.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 7

7. CHECK (C850) BLOWER SWITCH POSITION SIGNAL CIRCUIT FOR AN OPEN




Measure the resistance of the (C850) Blower Switch Position Signal circuit between the A/C Heater Control C1 harness connector and the A/C Heater Control C3 harness connector.

Q: Is the resistance below 5.0 ohms?

YES: Replace the A/C Heater Control.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Repair the (C850) Blower Switch Position Signal circuit for an open.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test

8. CHECK THE (C850) BLOWER SWITCH POSITION SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE




Turn the ignition off.
Disconnect the A/C Heater Control C1 harness connector.
Turn the ignition on.
Measure the voltage of the (C850) Blower Switch Position Signal circuit at the A/C Heater Control C3 harness connector.

Q: Is the voltage above 0.2 volts?

YES: Repair the (C850) Blower Switch Position Signal circuit for a short to voltage.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Replace the A/C Heater Control.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test

9. CHECK FOR NORMAL A/C MODE SWITCH & STATUS INDICATOR FUNCTION
Turn the ignition off.
Reconnect the A/C Heater Control C3 harness connector.
Turn the ignition on.
Turn the Blower control on.
Press the A/C mode switch on and off several times while observing the A/C status indicator.

Q: Does the A/C status indicator turn on and off with respect to the switch position?

YES: Go To 10
NO: Replace the A/C Heater Control.
Perform BODY VERIFICATION TEST - VER 1. Body Verification Test

10. CHECK A/C HEATER CONTROL OPERATION BY ATTEMPTING TO ENTER DIAGNOSTIC MODE
If illuminated, turn off the A/C status indicator and the EBL status indicator.
Actuate the display DTC function by performing the following:
- Turn the blower control on.
- Press the A/C mode switch down, turn the blower control to off, wait until both LEDs illuminate (approximately 5 seconds) and then release the A/C mode switch.

When entry mode is recognized, the A/C status indicator and the EBL status indicator will illuminate for 5 seconds and then display DTCs, if present. The A/C status indicator displays active DTCs when the EBL status indictor is not illuminated and stored DTCs when the EBL status indicator is illuminated. However, if no DTCs are present, both status indicators will turn off and the system will exit diagnostic mode.

Q: Did the A/C Heater Control enter diagnostic mode?

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