Chevrolet Silverado / GMC Sierra. Manual

Circuit/System Description

The steering angle sensor supplies input circuits to the electronic brake control module (EBCM)
from the Phase A and Phase B, the Index Pulse Phase C circuits, and 1 Analog signal circuit for
steering wheel angle. The analog signal is used along with the index pulse to calibrate the steering
angle sensor (SAS). The SAS position is then determined by Phase A and Phase B signals. The 2
input signals Phase A and Phase B are approximately 90 degrees out of phase. Once calibrated,
the EBCM dynamically interprets the relationship between the Phase A and Phase B inputs, and
determines the position of the steering wheel and the direction of the steering wheel rotation.

Conditions for Running the DTC

The ignition is ON.

Ignition voltage is greater than 9.5 volts.

Conditions for Setting the DTC

Opens, short to ground, or voltage on the analog signal circuits.

The calculated steering angle from the steering angle sensor does not correlate with the
steering angle calculated from the yaw rate.

Action Taken When the DTC Sets

The EBCM disables the Vehicle Stability Enhancement System (VSES) for the duration of
the ignition cycle.

The driver information center (DIC) displays the Service Stability System message.

The Antilock Brake System (ABS) remains functional.

The VSES Caution indicator turns ON.

Conditions for Clearing the DTC

The condition for the DTC is no longer present.

The EBCM automatically clears the history DTC when a current DTC is not detected in 100
consecutive drive cycles.

Diagnostic Aids

During diagnosis, park the vehicle on a level surface.

Inspect the vehicle for proper alignment. The vehicle should not pull in either direction
while driving straight on a level surface.

Find out from the customer the conditions under which the DTC was set. This information

2008 Chevrolet Silverado 1500

2008 BRAKES Antilock Brake System - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

will help to duplicate the failure.

The snapshot function on the scan tool can help find an intermittent DTC.

Reference Information

Schematic Reference

Antilock Brake System Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

ABS Description and Operation (With JL4) or ABS Description and Operation (Without
JL4)

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information.

Circuit/System Verification

With scan tool installed, clear the DTCs. Turn the steering wheel through its full range and back
to straight ahead to center SAS. Using a scan tool, observe the Steering Wheel position parameter
changes smoothly while turning steering wheel through the entire range. Correlate zero reading
with wheels in the straight ahead position. Drive the vehicle through a variety of maneuvers
turning to the left, and to the right and straight at a speed greater than 20 km/h (13 mph).

If the DTC did not set as a current DTC see diagnostic aids.

Circuit/System Testing

2008 Chevrolet Silverado 1500

2008 BRAKES Antilock Brake System - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

1. Ignition OFF, disconnect the harness connector at the SAS.

2. Test for less than 2.0 ohm of resistance between the low reference circuit terminal 2 and

ground.

If greater than the specified range, test the low reference circuit for an open/high
resistance. If the circuit tests normal, replace the EBCM.

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 1 and

ground.

If less than the specified range, test the 5-volt reference circuit for a short to ground or
an open/high resistance. If the circuit tests normal, replace the EBCM.

4. Test for 4.8-5.2 volts between the 5-volt reference circuit terminal 1 and the signal circuit

terminal 6.

If less than the specified range, test the signal circuit for an open/high resistance. If the
circuit tests normal, replace the EBCM.

5. Ignition OFF, reconnect the SAS.

6. Disconnect the EBCM harness connector.

7. Test for infinite resistance between the signal circuit pin 6 and ground.

If less than the specified range, test the signal circuit for a short to ground.

8. Disconnect the SAS.

9. Reconnect the EBCM harness connector.

10. Ignition ON, test voltage of phase A phase B, and phase C. verify that the reading is battery

positive voltage for each of the three phases.

If not the specified value, test the phase A phase B, and phase C circuits for a short to
ground or an open/high resistance. If the circuit tests normal, replace the EBCM.

11. Ignition OFF, reconnect the SAS. Turn the ignition ON. Using the scan tool, rotate the

steering wheel and observe the SAS. Verify the sensor sweeps through the entire range
while monitoring the steering wheel as it rotates in degrees from the input signals between
circuit phase A and the signal circuit phase B. The rotation in degrees should vary between
phase A and phase B without any spikes or dropouts.

If not within the specified range or is erratic, replace the steering angle sensor.

12. If the sensor test normal, replace the EBCM.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Electronic Brake Control Module Replacement (JH6, JH7) or Electronic Brake

2008 Chevrolet Silverado 1500

2008 BRAKES Antilock Brake System - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Control Module Replacement (JD9, JF3, JF7)

Control Module References for EBCM replacement, setup, and programming

DTC C0550

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC C0550 00