GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2006 🢒 Grand Am 🢒 Brakes 🢒 Antilock Brake System 🢒 DTC C1221-C1235

Circuit Description

As the wheel spins, the wheel speed sensor produces an AC signal. The electronic brake control module (EBCM) uses the frequency of the AC signal to calculate the wheel speed.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC C1221 Left Front Wheel Speed Sensor Input Signal = 0
    • DTC C1222 Right Front Wheel Speed Sensor Input Signal = 0
    • DTC C1223 Left Rear Wheel Speed Sensor Input Signal = 0
    • DTC C1224 Right Rear Wheel Speed Sensor Input Signal = 0
    • DTC C1225 Left Front Excessive Wheel Speed Sensor Variation
    • DTC C1226 Right Front Excessive Wheel Speed Sensor Variation
    • DTC C1227 Left Rear Excessive Wheel Speed Sensor Variation
    • DTC C1228 Right Rear Excessive Wheel Speed Sensor Variation
    • DTC C1232 Left Front Wheel Speed Sensor Circuit Open or Shorted
    • DTC C1233 Right Front Wheel Speed Sensor Circuit Open or Shorted
    • DTC C1235 Right Rear Wheel Speed Sensor Circuit Open or Shorted

Conditions for Running the DTC

C1221 through C1228

    • DTCs C1232 through C1235 are not set.
    • The brake pedal is not pressed.
    • The ABS is not active.

C1232 through C1235

The ignition is ON.

Conditions for Setting the DTC

C1221 through C1224

There are two groups of conditions under which these DTCs could be set. In each group, all of the listed conditions must be met.

All of the following conditions exist for 2.5 seconds:

    • The suspect wheel speed equals zero.
    • The other wheel speeds are greater than 8 km/h (5 mph).
    • The other wheel speeds are within 11 km/h (7 mph) of each other.

Or, all of the following conditions exist for 20 seconds:

    • The suspect wheel speed and a second wheel speed both equal zero.
    • The remaining two wheel speeds are greater than 16 km/h (10 mph).
    • The difference between the remaining two wheel speeds is less than 11 km/h (7 mph).

C1225 through C1228

The EBCM detects a rapid variation in the wheel speed. The wheel speed changes by 16 km/h (10 mph) or more in 0.01 second. The change must occur 3 times with no more than 1 second between occurrences.

C1232 through C1235

One of the following conditions exists for 0.02 seconds:

    • A short to voltage - the wheel speed sensor signal circuit or the wheel speed sensor return circuit voltages are greater than 4.25 volts.
    • A short to ground - the wheel speed sensor signal circuit or the wheel speed sensor return circuit voltages are less than 0.75 volts.
    • An open - the wheel speed sensor signal circuit voltage is greater than 4.25 volts and wheel speed sensor return circuit voltage is less than 0.75 volts.

Action Taken When the DTC Sets

If equipped, the following actions occur:

    • The EBCM disables the ABS/TCS for the duration of the ignition cycle.
    • The EBCM temporarily suspends the TIM monitoring function while the DTC is set.
    • The ABS indicator turns ON.
    • The Traction Off indicator turns ON.
    • The DRP does not function optimally unless a DTC for the other wheel speed sensor on the same axle is also set, then the EBCM disables the DRP for the duration of the ignition cycle.
    • When the EBCM disables DRP, the red Brake warning indicator turns ON.

Conditions for Clearing the DTC
    • The condition for the DTC is no longer present and the DTC is cleared with a scan tool.
    • The electronic brake control module (EBCM) automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Diagnostic Aids

C1221 through C1224

Under the following conditions, 2 Wheel Speed Sensor Input is 0 DTCs are set:

    • The 2 suspect wheel speeds equal zero for 20 seconds.
    • The other wheel speeds are greater than 16 km/h (10 mph).
    • The other wheel speeds are within 11 km/h (7 mph) of each other.

Diagnose each wheel speed sensor individually.

C1225 through C1228

A possible cause of this DTC is electrical noise on the wheel speed sensor harness wiring. Electrical noise could result from the wheel speed sensor wires being routed to close to high energy ignition system components, such as spark plug wires.

C1232 through C1235

If the customer comments that the ABS indicator is ON only during moist environmental conditions: rain, snow, vehicle wash, etc., inspect the wheel speed sensor wiring 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. Spray the suspected area with a 5 percent saltwater solution. To create a 5 percent saltwater solution, add 2 teaspoons of salt to 8 fl oz of water (10 g of salt to 200 ml of water).
  2. Test drive the vehicle over various road surfaces: bumps, turns, etc., above 40 km/h (25 mph) for at least 30 seconds.
  3. If the DTC returns, replace the suspected wheel speed sensor or repair the wheel speed sensor wiring.
  4. Rinse the area thoroughly when completed.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step measures the resistance of the wheel speed sensor in order to determine if the sensor has a valid resistance value.

    2.

  2. This step ensures that the wheel speed sensor is generating a valid AC voltage output.

Step

Action

Value(s)

Yes

No

Schematic Reference: Antilock Brake System Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Install a scan tool.
  2. Turn ON the ignition.
  3. Set up the scan tool snap shot feature to trigger for this DTC.
  4. Drive the vehicle at a speed greater than the specified value.

Does the scan tool indicate that this wheel speed DTC set?

8 km/h (5 mph)

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

3
  1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  2. Disconnect the wheel speed sensor connector.
  3. Measure the resistance across the wheel speed sensor.

Does the resistance measure within the specified range?

Front: 1040-1160 ohms

Rear: 1044-1276 ohms

Go to Step 4

Go to Step 8

4

  1. Spin the wheel.
  2. Measure the AC voltage across the wheel speed sensor.

Does the AC voltage measure greater than the specified value?

100 mV

Go to Step 5

Go to Step 8

5

Inspect for poor connections at the harness connector of the wheel speed sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 6

6
  1. Disconnect the electronic brake control module (EBCM) harness connector.
  2. Install the J 39700 Universal Pinout Box using the J 39700-99 Cable Adapter to the EBCM harness connector only.
  3. Test the wheel speed sensor circuits for the following:
    4. • An open
    • A short to ground
    • A short to voltage
    • Shorted together

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 7

7

Inspect for poor connections at the harness connector for the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 9

8

Replace the wheel speed sensor. Refer to Front Wheel Bearing and Hub Replacement in Front Suspension or Rear Wheel Bearing and Hub Replacement in Rear Suspension.

Did you complete the repair?

--

Go to Step 10

--

9

Replace the EBCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the repair?

--

Go to Step 10

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10
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK