C1221

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Circuit Description
The rotational movement of the toothed ring past the wheel speed sensor causes a change in the electromagnetic field which produces an AC voltage signal by the wheel speed sensor. The frequency of the sinusoidal (AC) voltage signal is proportional to the wheel speed. The amplitude of the AC voltage signal is directly related to wheel speed and the proximity of the wheel speed sensor to the toothed ring. The proximity of the wheel speed sensor to the toothed ring is also referred to as the air gap.

Conditions For Setting The DTC
DTC C1221 can set when the vehicle is not in an ABS stop.
A malfunction exists if both of the following conditions occur:
^ The left front wheel speed sensor input signal equals zero.
^ The vehicle's reference speed is greater than 8 km/h (5 mph)

Action Taken When The DTC Sets
^ A malfunction DTC stores.
^ The ABS/TCS disables.
^ The amber ABS/TCS warning indicators turn on.

Conditions for Clearing The DTC
^ The condition responsible for setting the DTC no longer exists and the Scan Tool Clear DTC function is used.
^ 100 drive cycles pass with no DTC detected.

Diagnostic Aids
The following conditions may cause an intermittent malfunction:
^ A poor connection
^ Rubbed-through wire insulation
^ A broken wire inside the insulation
Use the enhanced diagnostic function of the Scan Tool in order to measure the frequency of the malfunction. Refer to the Scan Tool manual or Scan Toot Diagnostics for the procedure.
If the customer's comments reflect that the amber ABS warning indicator is on only during moist environmental changes (rain, snow, vehicle wash), inspect all of the wheel speed sensor circuitry for signs of water intrusion. If the DTC is not current, clear all DTCs and simulate the effects of water intrusion by using the following procedure:
1. Add two teaspoons of salt to twelve ounces of water to make a five percent saltwater solution.
2. Spray the suspected area with the five percent saltwater solution.
3. Test drive the vehicle over various road surfaces (bumps, turns, etc.) above 24 km/h (15 mph) for at least 30 seconds.
4. If the DTC returns, inspect the suspected circuits.
Thoroughly inspect any circuitry that may be causing the intermittent complaint for the following conditions:
^ Backed out terminals
^ Improper mating
^ Broken locks
^ Improperly formed or damaged terminals
^ Poor terminal-to-wiring connections
^ Physical damage to the wiring harness
^ Corrosion and/or water intrusion of terminals.

Important: Difficulty may occur when trying to locate the intermittent malfunctions in the wheel speed sensor. Do not disturb any of the electrical connections. Change electrical connections only when instructed to do so by a step in the diagnostic table. Changing the electrical connections at the correct time will ensure that an intermittent electrical connection will not be corrected until the source of the malfunction is found.

Front Wheel Speed Sensor Resistance
Resistance of the wheel speed sensor will increase with an increase in sensor temperature.





The following table contains resistance values for the front wheel speed sensors at varying temperatures for use in diagnosis. The values are approximate and should be used as a guideline for diagnosis.

Important: Zero the J39200 test leads before making any resistance measurements.