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Fault Code 42 - Auto shutdown relay circuit
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Code 42 indicates a problem with the auto shutdown relay circuit. It is intended to indicate a bad connection on the ASD relay.

In general, if there is no complaint about engine stalling, this code may not be important. The computer will set this fault if it detects a sudden change in frequency from the engine speed sensor, crankshaft position sensor, and/or camshaft position sensor. If someone revs the engine and then pops the clutch too suddenly the computer may set 42 as a response to a near stall.

There are four wires running to the ASD relay:



Common Feed
Coil Ground
Coil Battery
Normally Open
Normally Closed


Diagnosis procedure:

First - unplug the relay and check socket pins 30 and 86 for correct voltages. If there is a problem, check the fuse feeding the pin. If the fuse is OK, use an ohm meter to check for a broken wire between the fuse and the relay.

Second - Unplug the relay and use and ohm meter to verify that the relay coil resistance is 75 ± 5 ohms by looking measuring between pins 85 and 86 on the relay. If the circuit is open or the resistance is too high, the relay coil is blown. If the resistance is too low, the coil is shorted. Replace the relay if the coil resistance in not within tolerance.

Third - remove the relay and look at the base terminals.

Fourth - Use an ohm meter to probe the Dark Blue/Yellow from Pin 85 to the terminal on the computer (see the service manual for the proper pin). The should be a very low resistance between the probes. If it is not, the wire is open. If the wire seems OK, wiggle the wire in several places to see if there is an intermittent connection.

Fifth - With the relay installed, turn on the ignition and probe the Dark Blue/Yellow at the computer. This wire should be at 0 volts. If it is not, suspect a computer problem.

Sixth - With the relay installed, turn on the ignition and probe the Light Green/Black wire at the computer (see the service manual for the proper pin). This wire should be at +12 volts. If it is not, replace the relay and check again. If it is still not reading +12 V, suspect a wiring break between the relay and the computer. NOTE: An intermittent problem with this wire or with the relay contacts may not set a fault code, but it will cause problems such as: stalling, under charging the battery, rough idle, stumble.

This page would not have been possible without the help of Hank LaViers,
who graciously loaned me his extensive Mopar engine library



Last Update: November 1, 2002