GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC C-Series Medium Duty Truck B7 🢒 DTC 🢒 DTC C0227 or C027 LF Wheel Speed Signal Erratic

Object Number: 339861 Size: MF
ABS Components
Antilock Brake System Schematics

Circuit Description

The wheel speed sensor coil emits an electromagnetic field. A toothed ring on the wheel passes by the wheel speed sensor and disrupts this electromagnetic field. The disruption in the field causes the wheel speed sensor to produce a sinusoidal (AC) voltage signal. The frequency and amplitude of the sinusoidal (AC) voltage signal are proportional to the speed of the wheel. The amplitude of the wheel speed signal is also directly related to the distance between the wheel speed sensor coil and the toothed ring. This distance is referred to as the air gap.

Conditions for Setting the DTC
    • The average wheel speed for all wheel speed signals is greater than 40 km/h (25 mph).
    • The average left front wheel speed is greater than 40 km/h (25 mph).
    • No speed signal input to the EBCM from the left front wheel speed sensor for 15ms. Anything which suddenly causes (intermittent) the left front wheel speed signal to drop to zero while the vehicle is moving greater than 40 km/h (25 mph).

Action Taken When the DTC Sets
    • The ABS indicator lamp turns on.
    • The ABS disables.

DTC C0227 is an Ignition Latched DTC, which indicates that the above actions remain true until the ignition is turned to OFF (even if the cause of the DTC is intermittent).

Conditions for Clearing the DTC
    • Repair the conditions responsible for setting the DTC.
    • Use the Scan Tool .

Diagnostic Aids

Any of the following conditions may cause an intermittent malfunction:

    • A poor connection
    • Wire insulation that is rubbed through
    • A wire breaks inside the insulation

Thoroughly check any circuitry that is suspected of 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

If the customer says that the ABS indicator lamp is on only during humid conditions such as rain, snow, or vehicle wash, then thoroughly inspect all wheel speed sensor circuits for signs of water intrusion. Use the following procedure:

  1. Spray the suspected area with a 5% salt water solution (two teaspoons of salt to 355 ml (12 oz.) of water).
  2. Drive the vehicle above 24 km/h (15 mph) for at least 30 seconds.

If the DTC returns, replace the suspected harness.

When inspecting a wheel speed sensor, inspect the sensor terminals and the harness connector for corrosion. If evidence of corrosion exists, then replace the wheel speed sensor. Refer to Front Wheel Speed Sensor Replacement .

Test Description

The numbers below refer to the steps in the diagnostic table:

  1. This step checks the EBCM 24-way connector for looseness, corrosion, etc.

    2.

  2. This step measures the resistance of the EBCM 24-way connector terminal 11 and terminal 23.

    3.

  3. This step measures the resistance at the left front wheel speed sensor connector.

    4.

  4. This step inspects the left front wheel speed sensor and the tone wheel for physical damage or excessive clearance.

Step

Action

Value(s)

Yes

No

1

Was the Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check - ABS

2

  1. Turn the ignition to OFF.
  2. Disconnect the 24-way EBCM harness connector from the EBCM.
  3. Inspect the harness connector for signs of damage or corrosion.
  4. Inspect the wheel speed sensor harness and the sensor harness connector for signs of damage or corrosion.

Are all the connections clean and tight?

--

Go to Step 3

Go to Step 6

3

Using aJ 39200 , measure the resistance between terminals 11 and 23 of the 24-way EBCM harness connector.

Is the resistance measurement within the specified range?

1500-2500 ohms

Go to Step 5

Go to Step 4

4

  1. Disconnect the wheel speed sensor from the wheel speed sensor harness connector.
  2. Using aJ 39200 , measure the resistance between terminal A and terminal B of the left front wheel speed sensor pigtail connector.

Is the resistance measurement within the specified range?

1500-2500 ohms

Go to Step 7

Go to Step 8

5
  1. Reconnect all the connectors.
  2. Verify that the left front wheel speed sensor is securely mounted and that the tone wheel is in good condition.

Are the wheel speed sensor and the tone wheel in good condition?

--

Go to Diagnostic Aids

--

6

Repair the 24-way EBCM harness connector if necessary.

Refer to Connector Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--

7

Repair the open or the high resistance in CKTs 830 or 873.

Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--

8

Replace the left front wheel speed sensor.

Refer to Front Wheel Speed Sensor Replacement .

Is the repair complete?

--

Go to Diagnostic System Check - ABS

--