F21 Abs not working (one wheel locked)

Make: Alfa Romeo
Model: 156 Factory Service Manual
Year: 1997–2002
Section: Brakes › F21 Abs not working (one wheel locked)

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Fault diagnosisF21 Abs not working (one wheel locked)

F21 Abs not working (one wheel locked)

When the brakes are operated abruptly without warning (panic braking), the ABS does not work and one wheel will therefore lock

NOTA: Locking of one wheel could - under certain circumstances - be a normal system reaction (see ABS operation). this is particularly likely on an unsurfaced road.

Step	Test procedure	Result	Action
0	PRELIMINARY CHECKS Turn the ignition on and check that the "ABS fault" warning light comes on for about 4 seconds, and then goes out.	OK	Move onto step 1
0		The "ABS fault" warning light comes on and stays on	Move onto step (see K60)
1	CHECK WITH DIAGNOSTIC EQUIPMENT Connect the diagnostic equipment (Examiner or other instruments) to the diagnostic socket Check: that there are no faults in the ABS control unit plausibility of all the parameters	OK	Move onto step 2
		An error is detected in the control unit	Continue according to the instructions for the diagnostic equipment End of diagnosis
		Lack of dialogue with the control unit	Restore the connection between the ABS control unit and the diagnostic connector (Wiring diagram E7020 ABS ). End of diagnosis
2	ACTIVE DIAGNOSIS WITH DIAGNOSTIC EQUIPMENT Using the diagnostic equipment (Examiner or other instruments) carry out the active diagnosis of: pump motor; solenoid valves; speed sensors	OK	Move onto step 3
		Fault detected in one solenoid	Replace electrohydraulic unit-electronic control unit Op. 3340A12 End of diagnosis
		Fault detected at the front	Replace the sensor Op. 3340A30 End of diagnosis
		Fault detected in a rear sensor	Replace the sensor Op. 3340A34 End of diagnosis
		Fault detected in a front wheel hub	Replace the wheel hub Op. 4450C28 End of diagnosis
		Fault detected in a rear wheel hub	Replace the wheel hub Op. 4450D10 End of diagnosis
3	AIR PRESENCE CHECK Check for presence of air in the system	OK	Move onto step 4
3		Presence of air in the system	Bleed the air from the system Op. 3330A14 End of diagnosis
4	CHECK CORRECT OPERATION Check that the fault is no longer present	OK	End of diagnosis
4		Fault persists	Incorrect selection of diagnostic procedure

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Parts & tools for this job For 1997 Alfa Romeo 156

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