C1202 Wheel Speed Sensor Front-LH Invalid/no Signal - Automotive Repair Guides & Equipment

COMPONENT LOCATION

GENERAL DESCRIPTION

The wheel speed sensor is the essential component the ABS ECU uses to calculate vehicle speed and to determine whether wheel lock occurs.

For example, rear wheel speed signal is used as a referecnce value, for vehicle speed, in front wheel drive vehicles, and if a difference between front and rear wheel speed occurs, then ABS control is performed.

Wheel speed sensor is active hall-sensor type.

DTC DESCRIPTION

The ABS ECU monitors the wheel speed sensor signal continuously.

This code is set when the sensor air gap is out of specified range or when the ABS control cycle is continued abnormally.

The HECU checks for air gap malfunctioning by monitoring the sensor signal at speeds between 2Km/h to 10 Km/h.

Warning lamp is turned OFF unless additional faults are detected when the IG KEY is turned ON again, and wheel speed is more than 10 Km/h (6.2mph).

DTC DETECTING CONDITION

Item

Detecting Condition

Possible cause

DTC Strategy

Signal monitoring

Improper installation of wheel speed sensor

Abnormal Rotor and wheel bearing

Faulty Wheel speed sensor

Case1
(Large Air-Gap)

Enable
Conditions

When the minimum wheel velocity is 2km/h and the velocity of other wheels exceed 10km/h (6.2mph) with the acceleration of < 0.4g, the controller start comparing the velocity of other wheels except the min. wheel. if their difference below 4km/h (2.5mph) is continued for 140msec, Otherwise, if their difference beyond 4km/h (2.5mph) or >0.4g is continued for 2 minutes.

In < 0.4g, when the velocity of more two wheels is 2km/h (1.2mph) and the max. wheel velocity exceeds 10km/h (6.2mph), the condition is continued for 20 sec. Otherwise, In >0.4g, the condition is 2 minutes.

After velocity of 4 wheel exceeds 10km/h (6.2mph), when velocity of 1 wheel or 2 wheel is 2km/h (1.2mph)and difference of other 2 wheel velocity is less than 4km/h (2.5mph) under that those velocity is more than 10km/h (6.2mph), if that conditions are continued for 12 seconds.

– This monitoring is performed for the period that the minimum velocity rises from 2km/h (1.2mph) to 10km/h (6.2mph).

Case2
(long term ABS mode)

Enable
Conditions

During the ABS control cycle, if the wheel velocity of 2km/h (1.2mph) is lasted for more than 12sec.

If the ABS control cycle is continued for more than 36sec.

Fail Safe

Only one wheel failure : Inhibit the ABS/ESP control, allow the EBD control. The ABS/ESP warning lamps are activated, the EBD warning lamp is not activated.

More than two wheels failure : The ABS/EBD/ESP functions are inhibited. The ABS/EBD/ESP warning lamps are activated.

SPECIFICATION

Sensor Type	Output Voltage		Airgap
	HIGH	LOW
Active Type	1.18~1.68V	0.59~0.84V	0.5~1.5mm

DIAGNOSTIC CIRCUIT DIAGRAM

SIGNAL WAVEFORM & DATA

Fig 1) Normal waveform of wheel speed sensor (Active type)

– High : Approx. 1.4V, Low : Approx. 0.7V

COMPONENT INSPECTION

■ Wheel speed sensor circuit check

1.	Lift the vehicle.

2.	Ignition “ON” & Engine “OFF”.

3.	Turn the wheel by hand.

Measure waveform between signal terminal of the wheel speed sensor harness connector and chassis ground with osciloscope.

High : 1.18~1.68V , Low : 0.59~0.84V

Is the measured waveform within specifications?

	▶ Fault is intermittent caused by faulty HECU, wheel speed sensor or external noise, an interference between harnesses. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage. Repair as necessary .
	▶ Check for improper installation of wheel speed sensor. If NG, repair as necessary and then go to “Verification of vehicle Repair” procedure. Check for damage of rotor teeth or wheel bearing. If NG, repair as necessary Substitute with a known-good Wheel speed sensor and check for proper operation. If problem is corrected, replace Wheel speed sensor

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