Starting The Cooldown Test - MTC System

WARNING: This page is about a different car, the 2005 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.

Once all of the prerequisites have been met, the Cooldown Test for the MTC system can be actuated by performing the following:

Fig 1: MTC System-Clearing DTCs And Cooldown Test

Courtesy of DAIMLERCHRYSLER CORP.

NOTE: 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. If this occurs, refer to *A/C HEATER CONTROL WILL NOT ENTER DIAGNOSTIC MODE (MTC) in ELECTRONIC CONTROL MODULES - ELECTRICAL DIAGNOSTICS for the diagnostic test procedure.

Verify that the ignition is in the Off position.
Turn the blower motor control (1) to the Off position.
Start the engine.
Press and hold the A/C mode switch (2) down and then turn the blower motor control to high speed. Continue to hold the A/C mode switch down until the A/C status indicator begins flashing, Then, release the mode switch.

Once actuated, the MTC A/C-heater control automatically positions the air-doors for optimal A/C performance and sends a request for A/C operation to the cluster (CCN) via hardwired circuits. The Cooldown Test can take up to two minutes to run. The test will stop running if any of the following occurs:

The ignition is turned to the Off position.
The blower motor control is turned to the any position other than high speed.
DTC 31 or 32 sets during the Cooldown Test.

While the Cooldown Test is running, the A/C status indicator will flash. During this time the A/C-heater control will ignore most of its inputs. If the MTC system passes the test, the A/C status indicator will stop flashing. However, if the MTC system fails the test, both the A/C and EBL status indicators will flash alternately and an active DTC 35 will set. The status indicators will continue to flash until either a successful Cooldown Test is executed or until the vehicle's ignition on time has exceeded a specified value. In addition, DTC 35 will remain active until a successful Cooldown Test is executed. Always check for and diagnose DTCs present in the A/C-heater control after running the Cooldown Test. If the Cooldown Test fails, service the heating-A/C system as required.