Heated Oxygen Sensor - Troubleshooting
Group: 24Number: 95-04
Date: Aug. 4, 1995
Subject:
Heated Oxygen Sensor, Troubleshooting
Model(s):
All Motronic Engine Management Systems m.y. 1993
Condition
A driveability complaint can lead to unnecessary replacement of the Heated Oxygen Sensor (H02S).
The following customer complaints and or observations may indicate a possible H02S problem.
^ Hesitation
^ Excessive visible exhaust smoke
^ Stalling and poor idle quality
^ CO outside specified range
^ Malfunction Indicator Lamp (MIL) Check Engine Light ON.
^ VAG 1551 Scan Tool displays, sensor malfunction
^ VAG 1551 Scan Tool displays, mixture control adjustment Diagnostic Trouble Code (DTC).
Oxygen sensor related complaints can be caused by:
^ Incorrect wiring combinations
^ Broken wires
^ Corroded terminals
^ Oxygen sensor heater not being energized (heater Relay not operating properly or supply Voltage interruption to sensor)
^ Contaminated sensor (e.g. Silicone, Antiseize compound etc.)
^ Malfunctioning Engine Coolant sensor (could cause the same complaints as Oxygen sensor)
^ Empty fuel tank or interrupted fuel supply
^ Vacuum leak or large exhaust leak upstream of the 02 sensor
^ Malfunctioning Engine Control Module
Service
Use the following steps to avoid unnecessary repairs when diagnosing suspected HO2S problems.
- Make sure you have enough information by answering the following questions.
- What is the symptom?
- Under what conditions does it occur?
- Is this the first repair for this complaint?
- Has any other work been recently performed on the car?
^ Basic and visual checks
- Check wires for slack. Check ground connections. Make sure all wiring harnesses are stress free, the wire insulation is not brittle and the insulation does not hide broken wires. If necessary perform voltage drop tests to verify connections.
- Check system for vacuum leaks.
^ VAG 1551 Scan Tool procedure:
To display DTC's relating to the HO2S control function you must drive the vehicle for a minimum of 10 minutes.
- Follow VAG 1551 connection and DTC memory check/erasing as described in the Fuel Injection and Ignition Repair Manual
- Remember to turn printer on and print the ECM version, (DTC's) and measuring block values.
- Read stored DTC'S, observe block values, and verify customer complaint.
If a DTC is stored, refer to the DTC table in the Fuel Injection and Ignition Repair Manual.
- Perform prescribed repairs, erase DTC memory and verify repair.
IF the vehicle has run out of fuel and the customer has complained of poor performance and a DTC appears (for example):
00537
Oxygen Sensor Control
Control limit exceeded
and
The adaptation value in Function 08, Display Group 06, Channel 2 is high (e.g.: 1.78).
THEN perform the following:
- Switch ignition OFF, disconnect ECM harness connector for approximately 1 minute, then reconnect.
- Interrogate DTC memory: if any DTC's are stored, repair and clear as necessary.
- Perform Engine Basic Setting (Function 04).
- Road test and check for DTC's and that the adaptation value, in Function 04, Display Group 06, Channel 2 is between .8 and 1.2
NOTE:
Use the following Labor operation for the above procedure:
24B1000 125 TU
If complaint still exists, perform the following:
- Ensure that the heater power wires (of the harness) match up to the white wires of the Oxygen sensor heater connection.
- Measure heating element resistance.
^ Must be approximately 2 Ohms.
Heated Oxygen Sensor heating circuit power supply, checking
- Disconnect the Heated Oxygen sensor harness connector.
- Connect VAG 1527B LED tester to harness connector using cables from VW1594 adapter kit. (Terminals 1 and 2).
- Start engine and let idle.
^ LED must light up.
If NO:
- Repair short/open circuit using wiring diagram.
Heated Oxygen sensor (HO2S) and Oxygen sensor control, checking.
- Test using VAG 1551 with engine idling.
- Perform Engine basic setting using repair procedures in Repair Group 01.
- Ensure that exhaust system is not leaking between three way Catalytic Converter and cylinder head.
- Ensure that voltage supply for Heated Oxygen sensor heater circuit is OK (see Perform Output Diagnostic Test Mode Function 03 step 9) (Engine not running).
- Go to "Read Measuring Value Block" Function (08) display group 01.
- Indicated on display (14=display field).
Read measuring value block 1
1 2 3 4
Continue testing only when:
^ Engine Coolant Temperature is over 80°C (176°F - channel 2).
^ Engine has run 2 minutes at idle.
- Read Oxygen Sensor factor in channel 3.
^ Value displayed must fluctuate up and down. If value in channel 3 does not fluctuate:
- Ensure that H02S heater is functioning properly.
- Briefly raise engine speed above 2000 rpm and repeat test.
- Press buttons -0-and-6- to select Function 06 "End Output".
- Press -Q- to confirm input.
If Oxygen sensor display does not change even during acceleration:
- Disconnect Heated Oxygen sensor harness connector.
- Connector adapter lead from VW1594 to cavity 4 (wiring to Motronic Engine Control Module J220) and hold to Ground (GND).
^ Value in channel 3 must increase. If YES:
- Replace Heated Oxygen Sensor.
If NO:
- Perform VAG 1598 Electrical test of wiring to H02S see Repair Group 01.
- Contact VW Technician Helpline if it is necessary to replace Motronic Engine Control Module (ECM) (J220).