Fault-Tracing Information
Fault-tracing
Checking vacuum system
Hint: Any diagnostic trouble codes stored in the engine control module (ECM) or forward sensing module (FSM) should be remedied first.
- Ignition on.
- Depress the brake pedal several times and check that it feels hard and responsive.
- Keep the brake pedal depressed and start the engine.
The brake pedal should travel and feel softer.
Was the function OK?
Yes - Checking brake pressure sensor
No - Checking vacuum system
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Checking brake pressure sensor
- Ignition on.
- Read off the pressure from the brake system.
The brake pressure must increase with increased pedal pressure.
If the brake pressure does not increase with increased pedal pressure, replace the brake system's hydraulic unit.
Other information:
Does the brake pressure increase?
Yes - Checking the component
No - Verification
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Checking the component
- Ignition off.
- Check the connectors of the brake control module (BCM) and the pressure build-up valve/pedal pressure sensor for contact resistance and oxidation.
- Reinstall the connectors, components etc.
- Ignition on.
- Activate the pressure build-up valve.
A mechanical noise should be heard from the engine compartment and the brake pedal should move slightly.
Is the function incorrect, check cables for open circuit, short-circuiting to ground as well as short-circuiting to voltage.
Take readings between:
- Brake control module (BCM) #31 (#A31) and pre-pressure valve #3.
- Brake control module (BCM) #17 (#A17) and pre-pressure valve #4.
Hint: Check the pressure build-up valve by (ignition off and pressure build-up valve/pedal pressure sensor's connector disconnected) measuring the resistance between the pressure build-up valve connector terminals #3 and #4. Resistance shall be approx. 3-5 ohms.
Other information
- Checking wiring and terminals Checking Wiring And Terminals
Was a fault detected?
Yes - Verification
No - Replacing a component
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Verification
Hint: After carrying out the repair, check that the fault has been remedied.
- Ignition off.
- Reinstall the connectors, components etc.
- Test drive the car as follows:
- Ignition on.
Read off the status of the diagnostic trouble code (DTC).
Is the status of the diagnostic trouble code (DTC) intermittent?
Yes - FAULT FOUND
No - Fault-tracing information
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Fault-tracing information
Attempt New Test - Checking vacuum system
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Replacing a component
Fault-tracing indicates an internal fault in the power brake booster. Replace the power brake booster.
If the diagnostic trouble code (DTC) recurs, replace the brake control module (BCM).
Other information:
- Anti-lock Brake System Module (ABS), L.H.D Anti-Lock Brake System Module (ABS)
Continue - Verification
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Checking vacuum system
Does the vehicle have a vacuum pump?
Yes - Checking the vacuum pump
No - Checking vacuum system
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Checking vacuum system
Check the vacuum and power brake booster's condition.
Were the hoses and the power brake booster OK?
Yes - Verification
No - Checking brake pressure sensor
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Checking the vacuum pump
Checking the vacuum pump
Fault-tracing information
Note! Fault tracing only applies to vehicles equipped with electrical vacuum pump.
The vacuum pump increases the brake booster's efficiency when the engine's vacuum pressure is too low, e.g., when the engine is off (ignition on).
Operating difficulties may make the brake pedal stiff.
Reasons for the vacuum pump not working can include:
- Open-circuit, short-circuit in the wiring to the vacuum pump.
- Defective switch for the vacuum pump.
- Defective vacuum pump.
Cause for vacuum pump running constantly can be:
- The cable to the vacuum pump is short-circuited to voltage.
- Defective switch for the vacuum pump.
- Defective hoses to the vacuum pump.
Continue - Checking the component
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Checking the component
Note! Fault tracing only applies to vehicles equipped with electrical vacuum pump.
- Ignition off.
- Check hoses and connections. Check for leakage.
- Before carrying out the next corrective action - wait approximately 3 minutes after switching the ignition off (system relay disconnected).
Pump the brake pedal a few times so that all negative pressure in the power brake booster disappears.
Check the vacuum pump's function by depressing the brake pedal with the ignition on. The vacuum pump must start and run for a few seconds to build up a new vacuum and then stop.
Select an option:
1. The vacuum pump functions normally.
2. The vacuum pump runs constantly.
3. The vacuum pump does not work.
Select an alternative.
1 - DONE
2 - Checking the wiring
3 - Checking the wiring
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Checking the wiring
- Ignition off.
Check the fuse for the vacuum pump in the integrated relay box and fusebox in the engine compartment. If the fuse has blown, check the power cable between the vacuum pump switch terminal #1 and the fuse. Check for an open-circuit. Check for a short-circuit to ground. Check the cable between vacuum pump switch terminal #2 and vacuum pump connector terminal #1. Check for an open-circuit. Check for a short-circuit to ground.
Check the function of the vacuum pump switch, with the ignition on, by temporarily connecting a cable, bridged between terminal #1 and #2 on the connector for the switch (vacuum pump side). If the vacuum pump starts, replace the switch.
If the vacuum pump does not start, read the resistance at vacuum pump terminal #1 and #2. If the resistance is infinite there is a short-circuit in the vacuum pump or in the cable between the vacuum pump and connector.
If the resistance is 0 ohms there is a short-circuit in the vacuum pump or in the cable between the vacuum pump and connector.
Remedy as necessary.
Other information:
- Checking wiring and terminals Checking Wiring And Terminals
Continue - Verification
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Checking the wiring
- Ignition off.
Check the power supply cable between the vacuum pump switch terminal #2 and the connector for vacuum pump terminal #1. Check for a short-circuit to voltage.
Hint: Check the switch for the vacuum pump by measuring the resistance between terminals #1 and #2. The resistance must be infinite.
Other information:
- Checking wiring and terminals Checking Wiring And Terminals
Continue - Verification
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Verification
Hint: After carrying out the repair, check that the fault has been remedied.
- Ignition off.
- Before carrying out the next corrective action - wait approximately 3 minutes after switching the ignition off (system relay disconnected).
Pump the brake pedal a few times so that all negative pressure in the power brake booster disappears.
Check the vacuum pump's function by depressing the brake pedal with the ignition on. The vacuum pump must start and run for a few seconds to build up a new vacuum and then stop.
Is the function OK?
Yes - FAULT FOUND
No - Fault-tracing information
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Fault-tracing information
Attempt New Test - Fault-tracing information
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FAULT FOUND - Verification
DONE - Checking brake pressure sensor
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