B1340

CIRCUIT DESCRIPTION

The heater and A/C programmer supplies voltage to an internal motor which drives the air mix door. The heater and A/C programmer monitors air mix door position feedback from a sensor on the motor. If the air mix door is requested to move but the feedback voltage does not change, the heater and A/C programmer stores DTC B1340. If the air mix door feedback indicates it is near the hot or cold extreme, the DTC will not set. Operation of the air mix door can be evaluated through self diagnostics as described in test description.

TEST CONDITION(S)

1. Commanded air mix door greater than 0%.
2. Commanded air mix door less than 76%.

FAILURE CONDITION(S)

1. Actual air mix door not within 3% of commanded air mix door position within approximately 60 seconds.

ACTION TAKEN

None.

TEST DESCRIPTION

1. A scan tool allows for direct control of the air mix door by observing the air mix door position sensor feedback value and its difference from the air mix door commanded position value.
2. These readings indicate a fault, internal to the heater and A/C programmer, in the air mix door sensor feedback.
3. If the door is not stuck, ensure smooth operation before replacing heater and A/C programmer.

NOTES ON INTERMITTENCE

If an intermittent DTC B1340 is being set, connect a scan tool and select snapshot data for air mix door # 1 and note value of feedback and commanded position. Using a scan tool override while monitoring feedback value, command the door to these positions. Without keying OFF, physically inspect the air mix door linkage for any obstruction at these positions.