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Audi 2.8L 5-Speed 1998 - Troubleshooting P1130, P1133, P1128, and P1137 Fuel Trim & O2 Sensor Codes

Model: Audi 2.8 5 spd 1998 Fault Code: P1128 Posted: 2007-08-29 18:22

Seeking expert advice on diagnosing and resolving the following OBD-II fault codes in my 1998 Audi 2.8L 5-speed manual transmission vehicle: P1130, P1133, P1-128, and P1137. These codes relate to fuel trim imbalances across Bank 1 and Bank 2, with specific issues including lean conditions in both banks, a rich condition on Bank 1, and an O2 sensor heating circuit malfunction. The vehicle is pre-OBD II, so diagnostic procedures may differ from modern models. I'm looking for clear, actionable steps to address these codes—especially since P1128 is known as a proprietary code common in Audi and VW vehicles. Any insights on root causes (such as MAF sensor failure or vacuum leaks) would be greatly appreciated before proceeding with part replacements.

Related fault codes
P1128P1130P1133P1137
Comments (5)
Anonymous 2007-08-30 09:00

Have you resolved the P1128 code yet? If this is a recently purchased vehicle with multiple fault codes, I'd recommend returning it to the dealer—Audi vehicles are generally not considered DIY-friendly, especially when dealing with complex fuel system diagnostics.

Anonymous 2007-08-30 11:58

I own three other Audi models, all pre-OBD II and CIS-based. While I've gained experience in DIY repairs for older Audis, I'm still seeking reliable information on these specific codes. If anyone has practical solutions—particularly regarding fuel trim imbalances or O2 sensor issues—it would save me significant troubleshooting time. Thanks for the response!

Anonymous 2007-08-30 12:50

Apologies for the delayed reply. P1128 is a proprietary code that activates when the long-term fuel trim reaches its maximum positive value—typically indicating a faulty Mass Air Flow (MAF) sensor. While VW and Audi have extended warranties to cover defective MAF sensors up to 7 years, before replacing the sensor, ensure there are no unmetered air leaks or broken vacuum hoses that could cause false readings. Always check for vacuum system integrity first as this is a common root cause.

Anonymous 2007-08-30 16:20

Fair point—having worked on several older Audis, I'd say you've covered the DIY side pretty well!

Anonymous 2007-12-31 15:14

P1128: Long Term Fuel Trim Max, Bank 1 system too lean P1130: Long Term Fuel Trim Max, Bank 2 system too lean P1133: O2 Sensor Heating Circuit malfunction, Bank 1 and Bank 2 Sensor 1 electrical fault P1137: Long Term Fuel Trim Add Fuel, Bank 1 system too rich