Vehicle: 2021 Jeep Grand Cherokee, 4WD, V6-3.6L, Automatic Transmission/Transaxle

Mileage: 77,095 miles

Problem: The customer stated that while the vehicle was being driven on the expressway at 75mph, the stability control, cruise control, park assist, malfunction indicator and service 4WD lights illuminated in the dash.

Case Details: A vehicle module scan showed the following diagnostic trouble codes (DTCs):

• U0403-00 - Anti Lock Brakes (Active)
• U148D-00 - Electric Power Steering (Stored)
• U0403-00 - Park Assist (Active)
• C2227-00 - Adaptive Cruise Control (Active)
• U148D-00 - Implausible Data Received from Forward Facing Camera (Stored)

On the test drive, the vehicle seemed to operate normally with no noticeable drivetrain noise. The service 4WD light was off at startup but illuminated after several minutes of driving. The technician noticed that the transfer case would not go into 4WD low and the light on the button would not illuminate.

When he got back to the shop, he contacted Tech-Assist for some diagnostic ideas. The consultant suggested confirming that the drivetrain control module (DTCM) was receiving 12 volts and that the ground going to the module was good. The technician measured 2.8 volts for Can Hi & 2.1 volts for Can Low at the module. The resistance check of the Can wires was good. He double-checked the main ground point under the hood, and everything appeared to be clean and tight. There was a 5-volt reference signal coming from the DTCM to the transfer case position sensor. A visual check of the wire harness in the cabin and underneath did not show any visible damage. Both battery cables were tight.

He found that the scan tool would not recognize or communicate with the DTCM. The technician cleared the DTCs, but they immediately came back. Based on the testing, the DTCM was determined to be bad.

Confirmed Repair: The technician installed a new DTCM, and everything went back to normal. All the systems worked, there were no more dash lights, no more codes, and the transfer case went into 4WD Low again. Problem Solved!