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.
1985 Porsche 928 StandardFACTORY OEM SERVICE PROCEDURE
Oxygen Sensor & LH Control Unit
- To check oxygen sensor, warm up engine to operating temperature. Check idle speed. Disconnect oxygen sensor plug. Connect voltmeter to ground and to the sensor wire (female plug). Reading should be .1-1.0 volts. If not, replace oxygen sensor.
- To check LH control unit, connect CO tester to one of the 2 test pipes in engine compartment. Warm up engine to operating temperature and check idle speed. Disconnect oxygen sensor plug. Recheck CO level. Connect oxygen sensor Green wire on plug to ground. If CO does not increase, check wire from LH control unit terminal 20 to oxygen sensor. If wire is okay, replace LH control unit.
Factory Service Tools
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no 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.