P1437 Cadillac A/C Evaporator Air Temperature Circuit High

Possible causes

ACET circuit open.

SIG RTN circuit open to the ACET sensor.

ACET circuit short to power (VREF).

Damaged ACET sensor.

Damaged PCM.

Tech description

The PCM sources a low current 5 volts on the ACET circuit (this voltage can be measured with the sensor disconnected). As the A/C evaporator air temperature changes, the ACET circuit resistance to SIG RTN (ground) changes (which changes the voltage the PCM detects). When the ACET signal is detected above the self-test maximum, check for open cirucits (ACET or SIG RTN), which would cause the voltage to remain high. Although not as probable, also check for a short to power (VREF).

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P1437 Cadillac Description

Indicates the ACET signal input was greater than the self-test maximum. The self-test maximum is 4.5 volts.