During initialization, the piston should reach the top of the cylinder resulting in a stalled motor. If the motor does not stall, the ABS control module will sense low current on the return circuit. This condition is most likely caused by a stripped nut or gear assembly. This condition will disable ABS and turn On the antilock telltale lamps.

Code 51 sets if:

Rear motor current is low and the motor is spinning freely.

Code 86 will also set.

This code can only set during initialization or at the end of an ABS stop.

Check gear assembly for a loose nut or worn sprocket.

When the ignition is cycled On, the ABS module verifies motors are in home position.

The ABS system will initialize (run motors down then up) when the vehicle is driven at least 13 km/h (8 mph) after start-up.

Diagnostics are run for this code every ignition cycle.

When attempting to diagnose an intermittent problem, use the Scan tool to review supplemental diagnostic information. The supplemental data can be used to duplicate a problem.

Select Malf History from Scan tool ABS menu.