C1227

C1225/C1226/C1227/C1228: Excessive Wheel Speed Variation







CIRCUIT DESCRIPTION
As wheel is rotated, wheel speed sensor produces an AC voltage whose frequency increases with wheel speed. EBCM uses frequency of the AC signal to calculate wheel speed. Speed sensor is connected to EBCM by a "twisted pair" of wires. Twisting reduces noise susceptibility, which may cause a DTC to set.

CONDITIONS FOR SETTING THE DTC
All of the following must be true for DTC to set.
^ DTC C1232, C1233, C1234 or C1235 not current.
^ Brake switch off.
^ Applicable wheel speed is accelerating or decelerating beyond reasonable limits.

ACTION TAKEN WHEN THE DTC SETS
^ ABS relay open, removing power from pump motor and solenoids.
^ Applicable DTC is stored.
^ ABS disabled, ABS warning light turns on.

DIAGNOSTIC AIDS
Thoroughly inspect wiring and connectors when diagnosing intermittent DTC(s). This will include the following.
^ Removal of protective conduit and inspection for wiring for damage, shorts and contamination.
^ Inspection for improperly formed and/or damaged terminals.
^ Checking terminal contact (retention force) by using a spare male/female terminal.
^ Removal of the terminals from the connectors to check for proper terminal to wire crimp.
If the drivers comments reflect that amber ABS warning light is on only during moist environmental changes (rain, snow, vehicle wash), all wheel speed sensor circuitry should be thoroughly inspected for signs of water intrusion. If the DTC is not current, simulate the effects of water intrusion. Use the following procedure. Spray suspected area with a 5 percent salt water solution. Then test drive the vehicle over various road surfaces such as (bumps, turns, etc.) above 24 kph (15 mph). If the DTC is set then replace suspected harness and/or sensor.
A careful visual inspection of the toothed ring for damaged such as cracks and tooth damage should be performed. If the DTC is set at the same speed every drive cycle, the toothed ring is most likely damaged.
Failure to perform the previous steps carefully and fully can result in misdiagnosis, unnecessary component replacement and reoccurrence of the DTC.

INSPECTION








NOTE: Diagnostic flow table must be performed first before using this table.
Type 1






Table 1 for Step 6





Table 2 for Step 7