Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSVOLVO1997850 L5-2.4L VIN 55 B5254SREPAIR AND DIAGNOSISA L L DIAGNOSTIC TROUBLE CODES ( DTC )TESTING AND INSPECTIONDIAGNOSTIC TROUBLE CODE DESCRIPTIONSMANUFACTURER CODE CHARTSENGINE CONTROL SYSTEMDETAILED DTC DESCRIPTIONSDTC EFI-522 REAR HEATED OXYGEN SENSOR HEATING
1997 Volvo 850 L5-2.4L VIN 55 B5254S
DTC EFI-522 Rear Heated Oxygen Sensor Heating
1997 Volvo 850 L5-2.4L VIN 55 B5254SSECTION DTC EFI-522 Rear Heated Oxygen Sensor Heating
5-2-1 FRONT HEATED OXYGEN SENSOR, HEATING
5-2-2 REAR HEATED OXYGEN SENSOR, HEATING
Trouble Code Conditions
- Monitoring of the heated oxygen sensor (HO2S) heating circuit begins approx. 3 minutes after the HO2S heating sequence starts. Diagnostic trouble code (DTC) EFI-521 or EFI-522 is stored if the engine control module (ECM) registers too high or low a current in the heating circuit.
Substitute value(s)
- Twin heated oxygen sensor fuel trim is disabled.
Possible source(s)
Signal too high:
- Short-circuit to supply voltage in signal cable.
- Defective heated oxygen sensor.
Signal too low:
- Short-circuit to ground in signal cable.
- Open-circuit in signal or power cable.
- Contact resistance in terminals.
- Defective heated oxygen sensor.
Fault symptom(s)
- None.
5-2-2 REAR HEATED OXYGEN SENSOR, HEATING
Trouble Code Conditions
- Monitoring of the heated oxygen sensor (HO2S) heating circuit begins approx. 3 minutes after the HO2S heating sequence starts. Diagnostic trouble code (DTC) EFI-521 or EFI-522 is stored if the engine control module (ECM) registers too high or low a current in the heating circuit.
Substitute value(s)
- Twin heated oxygen sensor fuel trim is disabled.
Possible source(s)
Signal too high:
- Short-circuit to supply voltage in signal cable.
- Defective heated oxygen sensor.
Signal too low:
- Short-circuit to ground in signal cable.
- Open-circuit in signal or power cable.
- Contact resistance in terminals.
- Defective heated oxygen sensor.
Fault symptom(s)
- None.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.