Antilock Braking System (ABS)

DTC 37 Rear Wheel Speed Sensor Circuit Continuity Malfunction:

CIRCUIT DESCRIPTION
The toothed wheel generates a voltage pulse as it moves past the sensor; each tooth-gap-tooth series on the wheel generates these pulses. The frequency of these pulses is used by the EBCM to determine wheel speed. The amount of voltage generated in each pulse depends on the air gap between the sensor and the toothed wheel, and on wheel speed.

DTC 37 WILL SET WHEN
There is a short to voltage or an open in CKT 1811 or 1810, or a malfunctioning speed sensor. The testing for this malfunction occurs with the ignition "ON" and the vehicle at rest.

ACTION TAKEN
Antilock braking is disabled. The ABS warning lamp will be "ON" for the remainder of the ignition cycle. If the malfunction is intermittent, the EBCM will enable the system at the next ignition cycle and a history DTC 37 will be present.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Checks for a short to battery in either of the speed sensor circuit wires.
2. Checks for an open in both the speed sensor circuit wires.
3. Manipulates wiring and connectors, trying to induce a intermittent malfunction not currently present.
4. This test checks if the DTC resets on key-up. If so, since tests 1-4 have validated that the circuitry and components are good, the speed sensor may be causing the malfunction.
5. Checks if DTC 35 sets during a road test.
6. DTC 37 sets when the vehicle is at rest; DTC 35 sets with a malfunction in the speed sensor circuitry with the vehicle in motion. If malfunctions are still present, DTC 35 would set during the road test, not a 37. If the DTC 37 sets at this point, the DTC 35 diagnostics should be used.
7. The wheel speed sensor may be causing an intermittent malfunction. If DTC 37 resets after sensor replacement, the EBCM must be concluding there is a malfunction present in the speed sensor circuit when there is not.
8. Ensures DTC was not set due to electromagnetic interference.

DIAGNOSTIC AIDS
Be sure the speed sensor wiring is properly routed and retained. This will help prevent false signals due to electrical noise being picked up by the wiring
It is very important that a thorough inspection of the wiring and connectors be performed. Failure to carefully and fully inspect wiring and connectors may result in misdiagnosis, causing part replacement with reappearance of the malfunction.