Diagnostic Strategies

Intermittent loss of power or ground to the EHCU:

Whenever diagnosing a 4WAL complaint, technicians should first ensure that the system is well grounded and has a stable power connection.

Any combination of the following code sequences are common indicators of intermittent loss of ground at the two pin connector on the EHCU:

Codes 73, 86
73, 86, 66
47, 66, 68, 48, 43, 44, 53, 54, 54, 86

The following code is an indicator of intermittent loss of power at the two pin connector on the EHCU:

Code 65

Other indications of possible intermittent losses of power or ground would include:

^ Difficulty in resetting the codes
^ Vehicle electrical abnormalities, particularly a malfunctioning heater fan motor, which shares the same power source with the 4WAL system
^ Evidence or knowledge of prior electrical repairs which might affect 4WAL system power or ground
^ Evidence of body or chassis damage which might affect 4WAL system power or ground






Wheel speed sensor circuit malfunction causing:

^ Premature EHCU activation with or without trouble codes being set
^ Customer complaints of antilock light flashing momentarily, but not remaining on. (Soft codes may be set)
^ Antilock light on and codes 28, 29, 31, 32, 33, 35, 36, 37, and/or 38 being present




Wheel speed sensor dropout (momentary interruption in sensor signal to EHCU) caused by:

^ Rear axle servicing that inadvertently damages speed sensor wires. (Intermittent short or open)
^ Air gap between sensor and tone wheel becomes enlarged beyond .05 inch
^ Loose, corroded or dirty connections at eight pin connector on EHCU
^ Faulty speed sensors