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Here’s the story. I got a 2009 C4S 6MT 2 weeks ago. I live in CA, but bought it from a friend in TX and had it shipped to me. When I went to get CA smog, I was told to go do the cat monitor drive cycle and then I would pass. The only modification is a fab speed air intake (no problem with visual inspection).
I read up on the cat monitor drive cycle and followed the advice on the forum. I got it to set on the first attempt. Feeling happy, I went for a 20 minute drive and then gassed the car up with 91 octane fuel. As soon as I left the gas station, the car was idling a little rough and my CEL came on. Having the OBD2 scanner with me from the drive cycle, I pulled over and did a proper scan. I got the following codes that seem to indicate the upstream bank 1 O2 sensor or something associated with it (see pics below). I cleared the codes and drove a little more, but the light came back on and it threw the same codes.
I’ve parked the car in my garage for now until I figure out what best steps to take. That leaves me pondering the following questions.
1. Could the cat monitor working properly have picked up another issue that was already there? The “all of a sudden” rough idle tells me probably not, but I don’t know.
2. Could the new fuel have done something to cause the rough idle and O2 sensor codes? One of the codes indicates the car is running rich.
3. Could it just be a cruel coincidence that the O2 sensor failed right after I successfully set the monitor and got it ready for a smog check?
4. The CEL is solid and not flashing, but is it safe to drive to the repair shop that is 13 miles away or should I tow it? If it appeared to be running fine I wouldn’t even second guess driving it, but I don’t want to foul any spark plugs and throw fuel onto my cat if that’s a legitimate risk.
This is a beautiful car that I just paid a lot of money for. It’s a bummer to have an issue already, but I don’t want to make it worse by being anxious to get it out on the road again. Any input is appreciated and I’m happy to finally be a legit member of the forum!
Been there done that. Put yourself out of your misery and get a PIWIS scan by a reputable shop. No other reader will do. In the meantime drive off in your Pcar and do an Italian tuneup. The cel likely won’t come on then.
M2CW
Johan
Been there done that. Put yourself out of your misery and get a PIWIS scan by a reputable shop. No other reader will do. In the meantime drive off in your Pcar and do an Italian tuneup. The cel likely won’t come on then.
M2CW
Johan
Yeah, the scan is what I need to do. I don't have the guts to do an Italian tuneup with the CEL on.
Hard to say what's going on there, but the fact that you're getting both a heater code and a sensor code on the same oxygen sensor suggests either the sensor is bad or you've got a wiring issue to it. It's entirely possible the sensor heater failed and the sensor isn't getting hot enough to give a good reading. May have been fine while driving but when the car sat during fueling it cooled down enough to throw a code. Just a guess, though.
Was it raining by any chance? Sometimes water can get into the heater connector and then no workie. Were it me I'd first verify the wires and connections to the bank 1 upstream oxygen sensor, and if those looked okay I'd just replace that sensor.
Hard to say what's going on there, but the fact that you're getting both a heater code and a sensor code on the same oxygen sensor suggests either the sensor is bad or you've got a wiring issue to it. It's entirely possible the sensor heater failed and the sensor isn't getting hot enough to give a good reading. May have been fine while driving but when the car sat during fueling it cooled down enough to throw a code. Just a guess, though.
Was it raining by any chance? Sometimes water can get into the heater connector and then no workie. Were it me I'd first verify the wires and connections to the bank 1 upstream oxygen sensor, and if those looked okay I'd just replace that sensor.
No, it wasn't raining at all. I cleared the codes and cold started it today. I didn't get it up to temp, but it idled fine and the only code that was popping was the P0132. Due to an upcoming vacation, I'm unfortunately going to have to just leave the car grounded for a couple of weeks until I get back to take it to a shop. I'm optimistic that it's nothing serious, just a pain to have to mess with it.
So, just replace the O2 sensor. They fail. I am not sure what the mystery is. Coincidences? I usually don't think so but I don't see this as a major fix... no?
What does the gas cap have to do with the O2 sensor?
It creates a vacuum leak into the system. Sometimes those show up as too lean because of the unmetered air entering but other times they show up as too rich because the O2 sensor sees the lean condition, adjusts the DME richer for more fueling to correct it and then you get a too rich code.
If replacing the O2 sensors, fully install them into the exhaust before plugging in the connector to the block to avoid twisting the wires.
It creates a vacuum leak into the system. Sometimes those show up as too lean because of the unmetered air entering but other times they show up as too rich because the O2 sensor sees the lean condition, adjusts the DME richer for more fueling to correct it and then you get a too rich code.
If replacing the O2 sensors, fully install them into the exhaust before plugging in the connector to the block to avoid twisting the wires.
In addition to this inspect the intake for any loose connections or any places a vacuum leak can occur past the MAF sensor. A vacuum leak (gas cap/lines etc) will allow unmetered air into the system, the ECU compensates for this increasing fuel to reach its target AFRs, causing a rich condition. Rough idle is an indicator of a vacuum leak also.
It creates a vacuum leak into the system. Sometimes those show up as too lean because of the unmetered air entering but other times they show up as too rich because the O2 sensor sees the lean condition, adjusts the DME richer for more fueling to correct it and then you get a too rich code..
A loose gas cap won't cause a vacuum leak, no. The car will run fine with the gas cap off, it's just that any leak in the tank system will leak fuel vapor and that's an environmental concern. So it's one of the things the OBD system checks for: there's a pump that occasionally pressures the tank to check for leaks.
It used to just throw a "check engine" light, and a loose fuel cap was generally the most common cause of that coming on. Nowadays most cars are smart enough to also give you a "check fuel cap" message for that one.
A vacuum leak would be an air leak in the intake plumbing between the MAF and the intake valves.
My .2 at 70K miles accurately threw a code identifying a vacuum leak in the fuel system which turned out to be a worn gas cap seal. Maybe .2 cars are a bit more sophisticated? My symptom of a bad cap was a CEL light on the dash that Durametric denoted as a "5504 Tank System Leak". I noted that the seal on the gas cap was a bit um.... "gritty".
Peace
Bruce in Philly (now Atlanta)
Last edited by Bruce In Philly; 06-20-2024 at 12:26 PM.
Yep, that's a leak but not a vacuum leak. A vacuum leak is a leak in the intake tubing: it's ambient air leaking into the intake system (which is at less than atmospheric pressure, hence the "vacuum" part). What you had there was a fuel vapor leak: it's fuel vapors leaking out of the pressurized fuel tank. The former will cause running problems, the latter will not. They'll both throw CELs but different ones.
I realize I'm being a tad pedantic here, but they're two very different things with very different impacts. "Vacuum leak" means something very specific, and what you had wasn't it.
06-18-2024, 01:02 AM
Question about O2 sensor situation
