DTC 27 Left Front Wheel Speed Sensor Continuity Fault

Toothed wheel generates a voltage pulse as it moves past sensor. EBTCM/EBCM uses these pulses to determine wheel speed. EBTCM/EBCM uses wheel speed sensor signal to calculate vehicle reference speeds and speed, acceleration and slip values for each wheel. These values are used to determine when anti-lock control is needed.

EBTCM/EBCM will only set one wheel speed sensor DTC at a time, even if multiple faults exist. Detection is prioritized accordingly: LF, RR, LR and RF. Check for additional stored DTCs after making repairs.

DTC 27 will set if there is a short to battery voltage or an open in circuits No. 830 or 873, or a faulty wheel speed sensor. DTC 25 may set if circuits No. 830 or 873 lose continuity and wheel speed sensor signal is lost while driving. DTC 27 should accompany this DTC on next ignition cycle. If DTCs 25 and 27 are set concurrently, diagnose DTC 27 first.

1. Checks for correct resistance in sensor.
2. Checks for a short to battery voltage in either speed sensor circuit wire.
3. Checks for an open in both speed sensor circuit wires.
4. Manipulates wiring and connectors, trying to induce an intermittent fault not currently present.
5. Checks if DTC resets at key on.
6. Checks if DTC 25 sets during road test.
7. DTC 27 sets when vehicle is at rest. DTC 25 sets with a problem in speed sensor circuitry with vehicle in motion.
8. Wheel speed sensor may be causing an intermittent fault.

Fig 1: DTC 27 Schematic

Courtesy of GENERAL MOTORS CORP.

Fig 2: DTC 27 Flow Chart

Courtesy of GENERAL MOTORS CORP.