FAQ - Check engine light comes on with EVO-CHR and THAR-CHR2.

Question

This FAQ applies to the EVO-CHR and THAR-CHR2 with the 2005-2007 Jeep Cherokee and 2007 Jeep Compass. Other vehicles using the EVO-CHR and THAR-CHR2 may be affected.

 

Problem:

The vehicles accessory (radio & heater) will oscillate on and off rapidly when the key has been inserted and turned to the ON/RUN position, after the vehicle has been remote-started and before the foot-brake has been pressed to shut down the remote-starter. In some cases a buzzing sound can be heard. This will cause the vehicles check engine light to come on.

The vehicles MUX wire is seeing two values at once. The first value is provided by the EVO-CHR during remote start and the second value is provided by the key when it is inserted and turned to the ON/RUN position. When these 2 values are provided in parallel together at the MUX wire, the combined value will  cause the MUX line to quickly oscillate the vehicle accessory causing the heater and radio to turn on and off rapidly. This in turn will cause the vehicle to throw a DTC (Diagnostic Trouble Code) and the vehicles check engine light will come on.

 

Solution:

Cut the vehicles MUX wire and insert a relay in series between the cut to isolate the MUX value from the key and from EVO-CHR from one another during remote-start key-takeover.

 

Wire the relay with the following connections:
Pin 85: GWR (Ground While Running).

Pin 86:Constant +12VDC.

Pin 87: MUX output from the EVO-CHR (White/Black).

Pin 87a: MUX ? towards the ignition plug (key-side).

Pin 30: MUX ? towards the BCM (vehicle-side).