Signal Too Low. Permanent Fault

Signal too low. Permanent fault

EFI-521 Front heated oxygen sensor (HO2S), preheating EFI-522 Rear heated oxygen sensor (HO2S), preheating

Checking power cable

- Ignition off.
- Disconnect heated oxygen sensor (HO2S) (front heated oxygen sensor (HO2S): black connector, rear heated oxygen sensor (HO2S): gray connector).
- Ignition on.

- Connect a voltmeter between heated oxygen sensor (HO2S) connector terminal 1 (main relay 2/32 side) and ground.

The voltmeter should read battery voltage.

OK - Checking the signal cable

Not OK - Checking for an open-circuit

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Checking for an open-circuit

- Check cable between heated oxygen sensor (HO2S) terminal 1 and main relay (2/32) terminal 3 for an open-circuit according to Checking wiring and terminals. Permanent fault Checking Wiring and Terminals. Permanent Fault.

Continue - Verification

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Checking the signal cable

- Ignition on.
- Heated oxygen sensor (HO2S) disconnected.

- Connect a voltmeter between the heated oxygen sensor (HO2S) connector terminal 2 (engine control module (ECM) side) and ground.

The voltmeter should read approximately 0 V.

OK - Checking signal cable resistance to ground

Not OK - Checking for a short-circuit

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Checking for a short-circuit

- Ignition off.
- Wait for approximately 150 seconds (cars with immobilizer 245 seconds).
- Heated oxygen sensor (HO2S) disconnected.
- Disconnect control module.

- Connect an ohmmeter between heated oxygen sensor (HO2S) connector terminal 2 (engine control module (ECM) side) and ground.

The ohmmeter should read infinite resistance.

OK - Connecting breakout box, A

Not OK - Checking for an open-circuit

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Checking for an open-circuit

- Check cable between heated oxygen sensor (HO2S) terminal 2 and engine control module (ECM) #A14 (for diagnostic trouble code (DTC) EFI-521)/ #A29 (for diagnostic trouble code (DTC) EFI-522) for a short-circuit to ground according to Checking wiring and terminals. Permanent fault Checking Wiring and Terminals. Permanent Fault.

Continue - Verification

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Connecting breakout box, A

Connecting breakout box, connector A

Connecting the breakout box

Is the breakout box connected to the Motronic 4.4 connector?

Yes - No Fault Found

No - Connecting breakout box to Motronic 4.4 connector A (black)

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Connecting breakout box to Motronic 4.4 connector A (black)
- Ignition off.
- Disconnect control module.

Note! The engine control module (ECM) must not be removed from the car until the main relay has interrupted its power supply. This may take up to 150 seconds (cars with an immobilizer 245 seconds) after the ignition has been switched off.

Connect adapter 951 1351 ADAPTOR 86-PIN 951 1351 Adaptor 86-Pin to engine control module (ECM) connector and connect breakout box 981 3190 Replaced by 9511428 981 3190 Replaced by 951 1428 to adapter.

Continue - Checking ground terminals

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Checking ground terminals

- Ignition off.
- Switch off all equipment that takes power from the battery (courtesy lighting, radio etc).
Connect an ohmmeter between battery negative terminal and:
- #13 (#A13) on the breakout box.
- #28 (#A28) on the breakout box.
- #42 (#A42) on the breakout box.

The ohmmeter should read approximately 0 ohms for all readings.

OK - Reading is OK

Not OK - Checking for an open-circuit

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Checking for an open-circuit

- Check ground terminals 31/32 and 31/33 at rear of engine and their cables for an open-circuit according to Checking wiring and terminals. Permanent fault Checking Wiring and Terminals. Permanent Fault and contact resistance and oxidation according to Checking wiring and terminals. Permanent fault Checking Wiring and Terminals. Permanent Fault.
- Check ground lead between engine and chassis for an open-circuit according to Checking wiring and terminals. Permanent fault Checking Wiring and Terminals. Permanent Fault and contact resistance and oxidation according to Checking wiring and terminals. Permanent fault Checking Wiring and Terminals. Permanent Fault.

Continue - No Fault Found

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Reading is OK
- Return to the fault-tracing procedure where it was interrupted.

Continue - No Fault Found

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FAULT FOUND - Checking signal cable resistance

No Fault Found - Checking signal cable resistance

FAULT-TRACING FAILED - Checking signal cable resistance

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Checking signal cable resistance

- Ignition off.
- Heated oxygen sensor (HO2S) disconnected.
- Control module disconnected.
Connect an ohmmeter between heated oxygen sensor (HO2S) connector terminal 2 (engine control module (ECM) side) and breakout box terminal:
- #14 (#A14), for diagnostic trouble code (DTC) EFI-521.
- #29 (#A29), for diagnostic trouble code (DTC) EFI-522.

The ohmmeter should read approximately 0 ohms.

OK - Checking heated oxygen sensor (HO2S)

Not OK - Checking for an open-circuit

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Checking for an open-circuit

- Ignition off.
- Connect the heated oxygen sensor (HO2S).
- Control module disconnected.
Connect an ohmmeter between breakout box terminals #27 (#A27) and:
- #14 (#A14), for diagnostic trouble code (DTC) EFI-521
- #29 (#A29), for diagnostic trouble code (DTC) EFI-522.

The ohmmeter should read 1.5 - 13 ohms.

OK - Checking connector

Not OK - Replacing component

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Checking connector

- The cause of the diagnostic trouble code (DTC) has been loose connections in the rear heated oxygen sensor (HO2S) connector. Check that the pins in the connector are intact.

Note! Do not apply rust solvent spray or grease to the heated oxygen sensor (HO2S) connector.

Continue - Verification

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Replacing component
- Try a new heated oxygen sensor (HO2S).

Continue - Verification

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Verification

Verification

Hint: After carrying out the repair, check that the fault has been remedied as follows.

- Ignition off.
- Front and rear heated oxygen sensors (HO2S) connected.
- Control module connected.
- Disconnect the Volvo Scan Tool (ST) from the VIDA station and use it in stand-alone mode.
- Start the engine and idle it.
- Go into verification menu.
Watch the diagnostic trouble code (DTC) to be verified.
Wait until its status switches to tested
This can take up to 5 minutes for EFI-521.
This can take up to 15 minutes for EFI-522.
- Read off diagnostic trouble codes (DTCs).

If EFI-521 or EFI-522 are stored they should intermittent fault status.

OK - VERIFIED

Not OK - VERIFICATION FAILED

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VERIFIED - FAULT FOUND

VERIFICATION FAILED - Fault-tracing information

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Fault-tracing information

Information

Fault-tracing information
The fault should have been detected and remedied. As this is not the case fault-tracing has failed.
Exit fault-tracing for this diagnostic trouble code (DTC) or make another attempt.

Do you want to exit fault-tracing?

Yes - Exit fault-tracing

No - Attempt New Test

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Attempt New Test - Checking power cable

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