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.
SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSVOLVO1993850 L5-2.4L VIN 55 B5254SREPAIR AND DIAGNOSISA L L DIAGNOSTIC TROUBLE CODES ( DTC )TESTING AND INSPECTIONMANUFACTURER CODE CHARTSEFI / DTC CODES (ENGINE CONTROL SYSTEM)DTC 2-1-2
1993 Volvo 850 L5-2.4L VIN 55 B5254S
DTC 2-1-2
1993 Volvo 850 L5-2.4L VIN 55 B5254SSECTION DTC 2-1-2
2-1-2 HEATED OXYGEN SENSOR SIGNAL
Condition(s) for DTC
^ The DTC is recorded if the Heated Oxygen Sensor (HO2S) signal does not vary from its mid-value (0.45-0.46 V) within 3 minutes after the engine temperature has exceeded 80°C (175°F).
Substitute value
^ The integrator is set to mid-range and the fuel trim function is inhibited.
Fault source(s)
^ Open-circuit in signal lead.
^ Faulty HO2S heater.
^ Faulty HO2S.
Fault symptom(s)
^ Fuel consumption may be high.
TESTING PROCEDURE
Status message
^ Check current Status Message.
If Status Message is: Permanent fault, signal faulty:
- Proceed to PERMANENT FAULT, SIGNAL FAULTY Section below.
If Status Message is: Intermittent fault, signal faulty:
- Proceed to INTERMITTENT FAULT, SIGNAL FAULTY Section below.
PERMANENT FAULT, SIGNAL FAULTY
Checking HO2S heater supply lead 2-pin connector
^ Switch ON ignition.
^ Disconnect HO2S heater connector (C/EF).
^ Connect voltmeter between HO2S heater connector (C/EF) terminal 1 (MFI module side) and ground.
Instrument should indicate battery voltage.
Checking HO2S heater supply lead 4-pin connector
^ Switch ON ignition.
^ Disconnect HO2S.
^ Connect voltmeter between HO2S connector (C/EP) terminal 1 (MFI module side) and ground.
Instrument should indicate battery voltage.
If reading is correct:
- Check HO2S heater signal lead.
If reading is incorrect:
- Check lead between main relay (2/32) terminal 3 and HO2S connector terminal 1 (2-pin, C/EF or 4-pin, C/EP) for open-circuit.
Checking HO2S heater signal lead, 2-pin connector
^ Switch ON ignition.
^ Disconnect HO2S heater.
^ Connect voltmeter between HO2S heater connector (C/EF) terminal 2 (MFI module side) and ground.
Instrument should indicate approx. 2 Volts.
Checking HO2S heater signal lead, 4-pin connector
^ Switch ON ignition.
^ Disconnect HO2S.
^ Connect voltmeter between HO2S connector (C/EP) terminal 2 (MFI module side) and ground.
Instrument should indicate approx. 2 Volts.
If reading is correct:
- Check HO2S heater element.
If instrument indicates approx. 0 Volts:
- Check resistance of signal lead to ground.
If instrument indicates over 5 Volts:
- Check lead between MFl module A28 and HO2S connector terminal 2 (2-pin, C/EF or 4-pin, C/EP) for short-circuit to supply.
Checking resistance of signal lead to ground, 2-pin connector
^ Switch OFF ignition.
^ Disconnect HO2S heater.
^ Connect ohmmeter between HO2S heater connector (C/EF) terminal 2 (MFI module side) and ground.
Checking resistance of signal lead to ground, 4-pin connector
^ Switch OFF ignition.
^ Disconnect HO2S.
^ Connect ohmmeter between HO2S connector (C/EP) terminal 2 (MFI module side) and ground.
If resistance is approx. 0 Ohms:
- Check lead between MFI module A28 and HO2S connector terminal 2 (2-pin, C/EF or 4-pin, C/EP) for short-circuit to ground.
If resistance is infinite (no continuity):
- Check lead between MFI module A28 and HO2S connector terminal 2 (2-pin, C/EF or 4-pin, C/EP) for open-circuit.
Checking HO2S heater element, 2-pin connector
^ Switch OFF ignition.
^ Disconnect HO2S heater.
^ Connect ohmmeter between HO2S heater connector (C/EF) terminals 1 and 2 (HO2S side).
Instrument should indicate 3 - 13 Ohms depending on temperature.
Checking HO2S heater element, 4-pin connector
^ Switch OFF ignition.
^ Disconnect HO2S.
^ Connect ohmmeter between HO2S connector (C/EP) terminals 1 and 2 (HO2S side).
Instrument should indicate 3 - 13 Ohms depending on temperature.
If reading is correct:
- Check HO2S signal lead.
If reading is incorrect:
- Try with new HO2S.
Checking HO2S signal lead, 2-pin connector
^ Switch ON ignition.
^ Disconnect HO2S connector (C/EE).
^ START engine.
^ Connect voltmeter between HO2S connector terminal 2 (MFI module side) and ground.
Instrument should indicate approx. 0.5 Volts.
Checking HO2S signal lead, 4-pin connector
^ Switch ON ignition.
^ Disconnect HO2S connector (C/EP).
^ START engine.
^ Connect voltmeter between HO2S connector terminal 4 (MFI module side) and ground.
Instrument should indicate approx. 0.5 Volts.
If reading is correct:
- Check HO2S.
If reading is approx. 0 Volts:
- Check lead between HO2S connector terminal 2 (2-pin, C/EE) or terminal 4 (4-pin, C/EP) and MFI module A22 for open-circuit.
^ Following repair of lead, check that HO2S is operating correctly.
^ Display DTC parameter list and read HO2S voltage.
Value should oscillate between 0.1 - 0.9 Volts with HO2S in circuit and hot, with engine idling.
Checking HO2S
^ Connect HO2S.
^ START engine.
^ Display DTC parameter list.
^ Read HO2S signal value.
Value should oscillate between approx. 0.1 and 0.9 Volts when HO2S is hot.
If reading is correct:
- DTC is due to poor contact in connector at HO2S. Check that connector pins are undamaged.
If reading does not oscillate:
- Try with new HO2S.
Note: HO2S connectors must not be packed with grease.
INTERMITTENT FAULT, FAULTY SIGNAL
Checking wiring and connections
Note: HO2S connectors must not be packed with grease.
^ Check lead between main relay (2/32) terminal 3 and HO2S connector terminal 1 (2-pin, C/EF or 4-pin, C/EP) for intermittent open-circuit.
^ Check lead between MFI module A28 and HO2S connector terminal 2 (2-pin, C/EF or 4-pin, C/EP) for intermittent open-circuit, intermittent short-circuit to ground or intermittent short-circuit to supply.
^ Check HO2S and MFI module connectors for loose connections.
^ Check lead between MFI module A22 and HO2S connector terminal 2 (2-pin, C/EE) or terminal 4 (4-pin, C/EP) for intermittent open-circuit.
Condition(s) for DTC
^ The DTC is recorded if the Heated Oxygen Sensor (HO2S) signal does not vary from its mid-value (0.45-0.46 V) within 3 minutes after the engine temperature has exceeded 80°C (175°F).
Substitute value
^ The integrator is set to mid-range and the fuel trim function is inhibited.
Fault source(s)
^ Open-circuit in signal lead.
^ Faulty HO2S heater.
^ Faulty HO2S.
Fault symptom(s)
^ Fuel consumption may be high.
TESTING PROCEDURE
Status message
^ Check current Status Message.
If Status Message is: Permanent fault, signal faulty:
- Proceed to PERMANENT FAULT, SIGNAL FAULTY Section below.
If Status Message is: Intermittent fault, signal faulty:
- Proceed to INTERMITTENT FAULT, SIGNAL FAULTY Section below.
PERMANENT FAULT, SIGNAL FAULTY
Checking HO2S heater supply lead 2-pin connector
^ Switch ON ignition.
^ Disconnect HO2S heater connector (C/EF).
^ Connect voltmeter between HO2S heater connector (C/EF) terminal 1 (MFI module side) and ground.
Instrument should indicate battery voltage.
Checking HO2S heater supply lead 4-pin connector
^ Switch ON ignition.
^ Disconnect HO2S.
^ Connect voltmeter between HO2S connector (C/EP) terminal 1 (MFI module side) and ground.
Instrument should indicate battery voltage.
If reading is correct:
- Check HO2S heater signal lead.
If reading is incorrect:
- Check lead between main relay (2/32) terminal 3 and HO2S connector terminal 1 (2-pin, C/EF or 4-pin, C/EP) for open-circuit.
Checking HO2S heater signal lead, 2-pin connector
^ Switch ON ignition.
^ Disconnect HO2S heater.
^ Connect voltmeter between HO2S heater connector (C/EF) terminal 2 (MFI module side) and ground.
Instrument should indicate approx. 2 Volts.
Checking HO2S heater signal lead, 4-pin connector
^ Switch ON ignition.
^ Disconnect HO2S.
^ Connect voltmeter between HO2S connector (C/EP) terminal 2 (MFI module side) and ground.
Instrument should indicate approx. 2 Volts.
If reading is correct:
- Check HO2S heater element.
If instrument indicates approx. 0 Volts:
- Check resistance of signal lead to ground.
If instrument indicates over 5 Volts:
- Check lead between MFl module A28 and HO2S connector terminal 2 (2-pin, C/EF or 4-pin, C/EP) for short-circuit to supply.
Checking resistance of signal lead to ground, 2-pin connector
^ Switch OFF ignition.
^ Disconnect HO2S heater.
^ Connect ohmmeter between HO2S heater connector (C/EF) terminal 2 (MFI module side) and ground.
Checking resistance of signal lead to ground, 4-pin connector
^ Switch OFF ignition.
^ Disconnect HO2S.
^ Connect ohmmeter between HO2S connector (C/EP) terminal 2 (MFI module side) and ground.
If resistance is approx. 0 Ohms:
- Check lead between MFI module A28 and HO2S connector terminal 2 (2-pin, C/EF or 4-pin, C/EP) for short-circuit to ground.
If resistance is infinite (no continuity):
- Check lead between MFI module A28 and HO2S connector terminal 2 (2-pin, C/EF or 4-pin, C/EP) for open-circuit.
Checking HO2S heater element, 2-pin connector
^ Switch OFF ignition.
^ Disconnect HO2S heater.
^ Connect ohmmeter between HO2S heater connector (C/EF) terminals 1 and 2 (HO2S side).
Instrument should indicate 3 - 13 Ohms depending on temperature.
Checking HO2S heater element, 4-pin connector
^ Switch OFF ignition.
^ Disconnect HO2S.
^ Connect ohmmeter between HO2S connector (C/EP) terminals 1 and 2 (HO2S side).
Instrument should indicate 3 - 13 Ohms depending on temperature.
If reading is correct:
- Check HO2S signal lead.
If reading is incorrect:
- Try with new HO2S.
Checking HO2S signal lead, 2-pin connector
^ Switch ON ignition.
^ Disconnect HO2S connector (C/EE).
^ START engine.
^ Connect voltmeter between HO2S connector terminal 2 (MFI module side) and ground.
Instrument should indicate approx. 0.5 Volts.
Checking HO2S signal lead, 4-pin connector
^ Switch ON ignition.
^ Disconnect HO2S connector (C/EP).
^ START engine.
^ Connect voltmeter between HO2S connector terminal 4 (MFI module side) and ground.
Instrument should indicate approx. 0.5 Volts.
If reading is correct:
- Check HO2S.
If reading is approx. 0 Volts:
- Check lead between HO2S connector terminal 2 (2-pin, C/EE) or terminal 4 (4-pin, C/EP) and MFI module A22 for open-circuit.
^ Following repair of lead, check that HO2S is operating correctly.
^ Display DTC parameter list and read HO2S voltage.
Value should oscillate between 0.1 - 0.9 Volts with HO2S in circuit and hot, with engine idling.
Checking HO2S
^ Connect HO2S.
^ START engine.
^ Display DTC parameter list.
^ Read HO2S signal value.
Value should oscillate between approx. 0.1 and 0.9 Volts when HO2S is hot.
If reading is correct:
- DTC is due to poor contact in connector at HO2S. Check that connector pins are undamaged.
If reading does not oscillate:
- Try with new HO2S.
Note: HO2S connectors must not be packed with grease.
INTERMITTENT FAULT, FAULTY SIGNAL
Checking wiring and connections
Note: HO2S connectors must not be packed with grease.
^ Check lead between main relay (2/32) terminal 3 and HO2S connector terminal 1 (2-pin, C/EF or 4-pin, C/EP) for intermittent open-circuit.
^ Check lead between MFI module A28 and HO2S connector terminal 2 (2-pin, C/EF or 4-pin, C/EP) for intermittent open-circuit, intermittent short-circuit to ground or intermittent short-circuit to supply.
^ Check HO2S and MFI module connectors for loose connections.
^ Check lead between MFI module A22 and HO2S connector terminal 2 (2-pin, C/EE) or terminal 4 (4-pin, C/EP) for intermittent open-circuit.
RENDER: 1.0x
NO RELATED
Recommended Tools & Savings
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
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.