S15/T15 2WD Jimmy V6-262 4.3L (1991)
Wheel Speed Sensor: All Technical Service Bulletins
ABS - Lamp Flashes/Codes Set Diagnostics
GMC NUMBER:
91-5E-11
GROUP:
5E ANTI-LOCK BRAKES
DATE:
AUGUST, 1990
CORPORATE
NUMBER:
065016
SUBJECT:
WHEEL SPEED SENSOR CIRCUIT MALFUNCTION
MODELS:
1990 M/L VANS AND, 1991 S/T 4 DOOR UTILITY VEHICLES WITH 4 WHEEL ANTI-LOCK BRAKES
PRIMARY INDICATORS OF SPEED SENSOR CIRCUIT MALFUNCTION The following items can be indications of malfunction in the speed sensor
circuit.
*
Premature EHCU (Electro Hydraulic Control Unit) activation (valve cycling during normal braking) WITH OR WITHOUT trouble codes relating
to sensor failures being set, is a strong sign of a wheel speed sensor circuit condition.
*
Customer comments of anti-lock light flashing momentarily but not remaining on (soft code may be set).
*
Anti-lock light on and one or more of the codes shown below are set.
DIAGNOSIS In the event of a wheel speed sensor malfunction on 4WAL equipped vehicles the EHCU may provide a means of determining which speed
sensor circuit may be the root cause. The following trouble codes identify a rear sensor condition.
Technicians should closely follow diagnostic fault trees given in RWAL UPDATE 4WAL PREVIEW manual 15005.05-1 mailed under cover Truck
Service Bulletin 90-5E-07 (Corporate Number 965008). Also the following guidelines may help isolate the cause of the problem. Any rear axle servicing
may inadvertently affect speed sensor signals if wires are accidentally shorted or the sensor to tone wheel air gap becomes larger than .05 inch. This
could cause premature anti-lock valve operation during normal braking. To check the sensor air gap and connector the wheel, brake hub and drum and
primary shoe must be removed. Refer to Truck Service Bulletin 90-5E-61 (Corporate Number 065003). For trouble codes which indicate a problem with
only one sensor, the entire sensor circuit from the 8 pin connector to the sensor should be checked for loose, corroded or dirty connections, shorted wires
and open circuits.
Speed sensor resistance, when taken at the connection on the sensor, should be 1000 to 2000 ohms. Resistance outside of this range would indicate a bad
sensor which would require replacement. Speed sensor resistance, when taken at the 8 pin connector (terminals A and H for right sensor and terminals D
and E for left sensor) should also be 1000 to 2000 ohms. Resistance measured outside of that range would indicate a short or open circuit. Speed sensor
output should be 1 volt AC when wheel is turned by hand 5 MPH minimum. Voltage should be checked at the 8 pin connector (terminals A and H for
right wheel sensor, terminals D and E for left wheel sensor).
For trouble codes which indicate a problem with more than one sensor the shared 8 pin connector is probably loose, broken or corroded.
