O2 sensor code question

[TonyMadrid]

Hi everyone,

I have a 2001 Grand Vitara and the check engine light came on. When I checked with a code reader it showed 8 codes (one for each of the four O2 sensors and an additional four of the same number codes, but indicated as pending codes). I was able to reset/erase all of the codes with the exception of the two upstream sensors.

So I replaced the two upstream sensors and when I stared the engine the check engine light was out, but at the next start it came on. When I checked the codes I got the same result as when I first checked it, i.e. eight codes. This time I was able to erase all of them, but at the next start the check engine light again came on.

Is there a time period needed for the codes to be able to properly reset, such as a number of starts? If not, where do I go from here?

Any help would be greatly appreciated.

Tony

[shorod]

There are several codes related to O2 sensors, and few of them state that the O2 sensor itself is necessarily faulty. Please post the exact code numbers. Since the pending codes are the same as the stored codes, no need to post each code twice, but at least post the 4 codes you're getting. Chances are good you have a vacuum leak or other issue causing codes for lean or rich conditions as reported by the O2 sensors, rather than the O2 sensors being the source of the code. Does the engine idle and run smoothly?

-Rod

[TonyMadrid]

Thanks for the reply. The codes were P0141, P0135, P0155, and P0161. The engine idles and runs smoothly.

Thanks,

Tony

[curtis73]

Here is my diagnosis. Three of them are heater codes which indicates that the relay or fuse for the O2 sensor heaters are dead. The last code is B2S2 low voltage. My guess is that B2S2 fried which took out the relay or the fuse. Test both the relay and fuse.

If you erase codes and the problem is fixed, it won't come back. The CEL is tripped after a certain frequency or duration of a fault. If you fix the problem and reset the light, it won't come back on because the problem no longer exists for that duration or frequency.

[TonyMadrid]

Hi Curtis,

All four codes are 02 sensor heater circuit malfunction codes The car belongs to a neighbor and I'll be checking it this afternoon. We were able to erase/reset the codes and the check engine light stays off until the next time the engine is started.

I'll check for a fuse or relay problem along with shorod's suggestion of checking for a possible vacuum leak.

Thanks again,

Tony

[shorod]

My comment of checking for vacuum leaks was before you posted what the codes were, reinforcing my point that there are several codes related to O2 sensors and the importance of posting the exact codes.

The description for all the codes is as follows, and applies to each of your 4 heated oxygen sensors (HO2S):

During testing the HO2S Heaters are checked for opens/shorts and excessive current draw. The test fails when current draw exceeds a calibrated limit and/or an open or short is detected.

Along with what Curtis73 mentioned, below are a few possible causes:

• Short to VPWR in harness or HO2S.
• Water in harness connector.
• Open VPWR circuit.
• Open GND circuit.
• Low battery voltage.
• Corrosion or poor mating terminals and wiring
• Damaged HO2S heater.
• Damaged PCM.

Start by checking the "free" things like corrosion/moisture in connections, then for shorts or opens if you have a wiring diagram for the vehicle. If the battery is nearing the end of its expected life, you might consider changing it out as preventive maintenance anyway. It's unlikely that all four sensors went bad at the same time so it also makes sense to start checking things that are common to all four sensors. Hopefully you have a good wiring diagram.

-Rod

[TonyMadrid]

Thanks for all the help guys. I found the problem - blown 15amp fuse. Valuable lesson learned - check other problem sources before changing the O2 sensors.

[shorod]

Glad you found the issue and it was (ultimately) an inexpensive fix. Also, THANK YOU for posting a follow-up with what you found. That's what makes these forums useful. Far too often folks come here for help, get what they need, then vanish until they have another issue, but never post what they found to help others.

-Rod