Common Vehicle Problems - No Communication

COMMON VEHICLE PROBLEMS - NO COMMUNICATION

If the scanner displays the message, NO COMMUNICATION. it means that the scanner and the logic module simply cannot communicate with each other for some reason. Some common problems that may prevent a Chrysler vehicle from performing a test or communicating with the scanner are listed below.

Check these points first:

1. Vehicle Identification - Check the vehicle identification entered from the characters on the VIN plate. If in doubt, re-enter the identification. If the vehicle identification is incorrect, the scanner may be unable to perform certain ATM or sensor tests or display computer data in the CODES & DATA mode.

2. Loss of power to the controller - Use the scanner READ J2 or FJ2 VOLTS test to check battery voltage supplied to the controller with the ignition on. The computer receives battery voltage through one or more fusible links in the wiring harness. Use a wiring diagram to check controller connections for battery voltage and ground. If a fusible link is open, the computer cannot communicate with the scanner. Also check the J1-J2 circuit splice near the controller.

3. Carbureted engines - failure to open the Idle stop (ground) switch - The idle stop (ground) switch on the carburetor must be held open to put the computer in the diagnostic mode. Be sure that the throttle stop screw is on the highest step of the fast-idle cam or place an insulator between the switch contacts. If a carbureted engine does not enter the diagnostic mode with the switch fully open, check for a shorted or open circuit in the switch wiring.

4. Fuel-Injected engines, 1988 and earlier: open or shorted auto shutdown (ASD) relay circuit - The scanner must be able to switch the ASD relay to perform ATM and sensor tests. If the circuit or the relay is open or shorted, the scanner cannot energize and de-energize the relay. The 1989 and later systems do not require ASD relay operation to run ATM and sensor tests.

5. Carbureted engines - open or shorted carburetor oxygen feedback solenoid circuit - The scanner must be able to switch the carburetor feedback solenoid on most carbureted engines to perform ATM and sensor tests. If the circuit or solenoid is open or shorted, the scanner cannot energize and deenergize the solenoid. Check a wiring diagram for a specific carbureted engine to determine if the carburetor solenoid or another solenoid is used to perform ATM and sensor tests.