← Back to list

P0136 and P0156 Fault Codes on 1999 Ford Taurus SE 3.0L DOHC: Downstream O2 Sensor Diagnosis

Model: 99 Taurus SE 3.0 DOHC Fault Code: P0136 Posted: 2011-09-30 19:02

My 1999 Ford Taurus SE 3.0L DOHC vehicle has been throwing out fault codes P0136 and P0156, indicating issues with both downstream oxygen (O2) sensors. When connected to a data logger, the Bank 1 sensors show normal voltage readings within expected ranges. However, both Bank 2 downstream O2 sensors remain stuck at 0 mV, showing no signal variation. I'm wondering if a failure in either or both of the Bank 2 sensors could trigger codes for both downstream O2 sensors. What is the most effective diagnostic approach to identify the root cause?

Related fault codes

P0136P0156

Comments (3)

Anonymous 2011-09-30 19:15

Start with a detailed wiring diagram and use a digital multimeter (DVOM) to check continuity and voltage at each sensor connector. It's highly unlikely that both downstream O2 sensors would fail simultaneously.

Anonymous 2011-10-01 09:13

Are the oxygen sensors wired in a loop configuration? If one sensor fails, could it cause the other to appear faulty? Additionally, I noticed the vehicle hesitates at low speeds and emits black soot from the exhaust—could this be related to the O2 sensor failure or fuel mixture issues?

Anonymous 2011-10-02 08:46

Both post-catalyst oxygen sensors are reporting circuit malfunctions. First, verify all relevant fuses and inspect the wiring harness according to Jeff's recommendation. The O2 sensors are wired in parallel, not in series, so a failure in one should not directly cause the other to fail.