DTC P0538: A/C Evaporator Temperature (ACET) Circuit High Input

WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.

P0538 - A/C EVAPORATOR TEMPERATURE (ACET) CIRCUIT HIGH INPUT

Description:	Indicates the ACET signal input is greater than the self-test maximum. The self-test maximum is 4.5 volts.
Possible Causes:	ACET circuit open. SIG RTN circuit open to the ACET sensor. ACET circuit short to power (VREF). Damaged ACET sensor.
Diagnostic Aids:	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 circuits (ACET or SIG RTN), which cause the voltage to remain high. Although not as probable, also check for a short to power (VREF).
Application	Key On Engine Off	Key On Engine Running	Continuous Memory
All	GO to Pinpoint Test DJ .