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.

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?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Trying to determine if a Honda 2005 vtec (D172A) sohc, 127 hp has an O2 upstream sensor problem or the ECU

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: How does the HomeLink® transceiver work?

If you drive an EX-L V6, then your car came standard with Honda’s HomeLink® universal transceiver. It’s a handy device that’s built right into your car and is designed to work with other things around your home, like your garage...

Q: Found oil leak when changing spark plugs

Hi there. This is very common on your vehicle. This is caused by the valve cover gasket tube seals. These fail all of the time because they become brittle as the engine gets older. Once that occurs, they start to...

Q: Loud pop and started running hot

A possibility is a head gasket leak where exhaust gas leaks into the cooling system pressurizing the cooling system and blowing out a hose. However, there are other potential, less serious, causes for what you describe. To get the actual...

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...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...