Oxygen Sensor General Information, Testing, and Replacement
How the O2 sensor works in single-wire and three-wire heated versions, how to test its response with a voltmeter, and factory Porsche and Bosch part numbers for all 944 and 968 variants.
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General Information
On 944s equipped with oxygen (O₂) sensors, the sensor measures oxygen content in the exhaust and feeds a signal to the DME so it can adjust the fuel mixture to achieve the correct air/fuel ratio. The O₂ sensor is also called a Lambda sensor.
When the DME is operating based on O₂ sensor feedback, this is referred to as closed loop operation. If the sensor is faulty or disconnected, the DME operates in open loop mode, using preset fuel maps derived from airflow measurements. 944 variants without O₂ sensors (many rest-of-world models) always operate in open loop from factory fuel maps.
Two sensor types were used:
- Single-wire (non-heated): Heated by exhaust gas; the single wire provides the output signal to the DME. The DME operates in open loop until the sensor reaches operating temperature.
- Three-wire (heated): One signal wire plus two wires that power an internal heater element. This reduces warm-up time significantly and shortens the open loop period.
General service intervals: heated sensors approximately 60,000 miles; non-heated sensors approximately 30,000 miles.
Symptoms of a failing O₂ sensor:
- Engine surges or hesitates
- Strong smell of fuel from the exhaust
- Poor fuel economy
- Failed emissions test (high CO or high HC)
- Premature catalytic converter clogging (if equipped)
Testing
- Start the car and run until the engine reaches normal operating temperature.
- Disconnect the O₂ sensor and connect a voltmeter to the sensor wiring plug.
- Run the engine at approximately 2500 rpm.
- Introduce propane into the intake to enrich the mixture until engine rpm drops by approximately 200 rpm. Alternatively, disconnect the vacuum line to the fuel pressure regulator — plug the disconnected manifold end to prevent an intake vacuum leak.
- If the voltmeter reading rapidly rises above 0.9 VDC, the sensor is correctly indicating a rich mixture. If response is sluggish or voltage remains below 0.8 VDC, replace the sensor.
- Remove the propane source (or reconnect the FPR vacuum line).
- While continuing to run at 2500 rpm, disconnect a vacuum line from the intake to lean the mixture.
- If the voltmeter rapidly drops below 0.2 VDC, the sensor is correctly reading a lean mixture. If response is sluggish or voltage stays above 0.2 VDC, replace the sensor.
Factory O₂ Sensor Part Numbers
| Porsche P/N | Bosch Short P/N | Bosch Long P/N | Model | Year | Wires | Heated | Service Interval |
|---|---|---|---|---|---|---|---|
| 944 606 133 00 | 11031 | 0 258 001 031 | 944 | 1983–1985.0 (49-state) | 1 | No | 30,000 mi |
| 944 606 135 00 | 13001 | 0 258 003 001 | 924S, 944 (1983–1988), 944S — California | 1983–1988 (California) | 3 | Yes | 60,000 mi |
| 944 606 135 02 | 13011 | 0 258 003 011 | 924S, 944 (1985.5–1988), 944, 944S, 944S2, 968 | 1985.5–1988 (49-state); 1989+ all; 944S all; 944S2 all; 968 all | 3 | Yes | 60,000 mi |
| 951 606 135 00 | 13012 | 0 258 003 012 | 944 Turbo | All | 3 | Yes | 60,000 mi |
Note: Bosch "short" part numbers are used for ordering. Bosch "long" part numbers are stamped into the sensor body.
Bosch Universal Replacement Part Numbers
| Bosch Short P/N | Bosch Long P/N | Description | Wires | Heated | Service Interval |
|---|---|---|---|---|---|
| 11027 | 0 258 001 027 | Universal replacement without connector (924, 924 Turbo, 928, 944 1983–1985.1) | 1 | No | 30,000 mi |
| 13913 | 0 258 003 913 | Universal replacement without connector — must be spliced to factory connectors (924S, 944 1985.5–1989, 944S, 944S2, 944 Turbo, 968) | 3 | Yes | 60,000 mi |
| 15735 | 0 258 005 735 | Universal replacement with connector kit — replaces stock connectors (924S, 944 1985.5–1989, 944S, 944S2, 944 Turbo, 968) | 3 | Yes | 60,000 mi |
General Installation Notes
Warning: Do NOT solder the wiring connectors onto a universal O₂ sensor. Crimped connections are required. The sensor draws fresh air along the stranded wire to its internal reference chamber — solder fills the wire strands and blocks this airflow, causing the sensor to malfunction.
Warning: Do not use silicone-based products (many RTV sealants, gasoline additives, and anti-seize compounds) near the O₂ sensor. Silicon contamination will destroy the sensor. Check product labels before use.
Replacement
- Locate and disconnect the O₂ sensor connector plug. On most cars this is a round connector at the rear of the engine. If the sensor has been previously replaced with a universal unit, the connector location may vary.
- Remove the sensor using a 15/16" (24 mm) open-end wrench or an O₂ sensor socket.
- If installing a universal sensor without a connector kit, splice the factory connector plug onto the new sensor wire using crimp-type connectors (do not solder).
- Install the new sensor and tighten.
- Reconnect the sensor connector.