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

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Acceleration issues and car dying

Hello. There are certain cases where an oxygen sensor can cause performance issues. It would depend on the specific trouble code. A few things I would look at are the specified oxygen sensor or circuit, the ignition coil, the ignition...

Q: I have a 2005 Lincoln navigator that the number 6 spark plug is misfiring on.

Hello. A misfire can be caused by a number of things. Depending on what they found to be the problem it is quite possible that this is an accurate estimate. Most of the time this is caused by a failure...

Q: car won't start, maybe electrical - 1995 Honda Civic

Hey there. I would start by checking the speed sensors. The plug that connects to this in the engine bay can become wet and can cause this type of problem. Also, check the alternator, and VSS (vehicle speed sensor) fuse...

Related articles

Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
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...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.