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P0136 Fault Diagnosis for 1999 Mustang (Non-GT) - Oxygen Sensor or Fuel System Issue?

Model: 1999 Mustang Fault Code: P0136 Posted: 2010-05-04 14:31

Hi everyone, I recently ran diagnostics on my 1999 Mustang (non-GT model) and received a P0136 fault code. The car has accumulated 180,000 miles, and I'm unsure whether to invest in repairs or consider it a minor issue. The vehicle has been exhibiting noticeable shaking, especially at idle and stoplights—this improves when driving on the highway. However, the P0136 code is still showing up. Here’s what the diagnostic report states: Troubleshooting for P0136 (Oxygen Sensor Bank 1 Sensor 2): - OEM Brand: Domestic - Probable Causes: aa1 - Oxygen sensor defective aa2 - Fuel system running very rich or lean — check other codes first aa3 - Engine misfire condition — repair required aa4 - Abnormal fuel pressure (high or low) — check fuel pump or pressure regulator As a high school senior, I’m not deeply familiar with automotive diagnostics. A technician at AutoZone suggested it might be the fuel pump, estimating $200 for parts without labor. However, I’d like to get more expert opinions before making any decisions. Thanks in advance! Jon

Related fault codes

P0136

Comments (4)

Anonymous 2010-05-04 21:08

AutoZone technician is incorrect — P0136 specifically refers to an oxygen sensor issue, not a fuel system lean or rich condition. This code points to Bank 1 Sensor 2 (passenger side, located behind the catalytic converter).

Anonymous 2010-05-05 05:40

Agreed — replace the O2 sensor on Bank 1, Sensor 2 (passenger side, behind the catalytic converter). This is a common fix for P0136 in 1999 Mustangs. Ensure you use OEM or high-quality aftermarket parts.

Anonymous 2010-05-05 08:42

Thanks for the clarification! Will replacing this sensor resolve both the shaking and increased fuel consumption? Are there any approximate costs for part and labor? Any advice on where to source it?

Anonymous 2010-05-05 11:00

Without physically inspecting the vehicle, we can’t guarantee results. However, consider purchasing the O2 sensor from an authorized dealer rather than a local auto parts store — quality matters. While this sensor may not significantly improve drivability, it could help stabilize fuel efficiency. The shaking and fuel consumption issues might stem from other problems too. Fuel trim data and readings from other sensors (like MAF or throttle position) would provide better insight. What engine type does your Mustang have? Does it have a K&N air filter installed upstream of the MAF sensor, which could interfere with fuel trims?