Skip the auto shop - Our mechanics make house calls

Q: Trying to determine if a Honda 2005 vtec (D172A) sohc, 127 hp has an O2 upstream sensor problem or the ECU

asked by on

I've taken voltage reading of both O2 sensors from the ECU connector(s) behind the glove box with digital multi-meter. Seems both initiate at 0.290v bias volts before the Htr circuit effect. Once heated, I observed the downstream sensor avg 0.4 v at idle and acceleration (+/- spikes). The upstream sensor avg 0.295v at idle and accl. With both sensors connected the engine idles fine but struggles on accl, power loss or hunting and when accl released, it gasp and sometime stalls out. When I disconn the upstrm O2 and leave the dwnstrm connected, the engine runs fine on idle and accl. When just upstream O2 connected, the engine runs bad as previously describe. I observed the readings on upstrm O2, it starts out at 0.290v - bias voltage then jumps up to 0.5 - 0.7 v (Htr ckt kicks in?) for a few seconds then drops and avg 0.290v. I notice before the Htr ckts effect (10s) with both sensors in, the engine had full pow at idle and accl. Took upstrm O2 rdg in open air, 0.75v - 0.9v, stable.

My car has 167920 miles.
My car has an automatic transmission.

A: Hello. From what you describe it would appe...

Hello. From what you describe it would appear that your upstream oxygen sensors are causing the issue. If you disconnect them and the vehicle runs better then it may very well be possible that the signal they are sending or generating may be a bad one, and confusing the computer, causing your performance issues. Keep in mind that the heater circuit and the signal circuit will usually be on separate wires, and should not kick on and off and change the signal of the sensor. Most oxygen sensors are designed to operate in cycles, however, if they are giving off erratic readings that may be a sign that the sensor is bad. I would try to get the specifics on what the sensor voltages should be for that vehicle and compare them with your findings to see what you may conclude. If you need a diagnostic, an expert from YourMechanic can come to your car’s location to inspect the loss of power issue to help guide you through repairs.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Engine hesitation a possible starter problem.

Long crank times are usually caused by lack of fuel pressure at the injectors, typically caused by stuck open fuel pressure regulator or a fuel pump on its way out. Have a mechanic from YourMechanic test fuel pressure and volume...

Q: Turn signal lights not working.

I believe there was a recall done on the turn signals for your vehicle. You may check with your local dealership and see if this applies to your vehicle. If not, these are cars are known for having faulty turn...

Q: I have a new battery but my car won't start

The solution will depend on the symptom you are observing as you try to start the car. I recommend a no-start diagnostic which will identify the root cause. There are a lot of possibilities but if the engine does turn...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...