Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Hi, guys. I have a 2006 Jeep Liberty 3.7 litre which has a CL fault on bank 2 and a DTC for high voltage on the downstream O2 on that side. Short and long fuel trims on that bank look okay.
I was unfamiliar on what a CL fault was so I looked it up and, according to the ONE article I was able to find on the subject, it apparently involves the PCM thinking there's a problem with the one of the upstream O2s. It went on to say that despite the hunch, the PCM still uses info on that sensor to adjust fuel trims and doesn't go into open loop or try to grab data from another banks' upstream.
I guess my question here is, is the definition I found on the CL fault correct? Also, could the high voltage code I'm getting on the the rear O2 be related to that fault? I guess my thinking there is that, for whatever reason, the PCM thinks the info it's getting from the rear O2's is more reliable than what it's getting from the upstream one.
"I guess my question here is, is the definition I found on the CL fault correct?"
Long and short answer. Yes. As long as you understand that a DTC alone does not mean that sensor is bad or is the source of the problem.
"Also, could the high voltage code I'm getting on the the rear O2 be related to that fault?"
Yes.
"I guess my thinking there is that, for whatever reason, the PCM thinks the info it's getting from the rear O2's is more reliable than what it's getting from the upstream one."
No.
The strategy of the downstream 02 is to protect the catalytic converter not that it's more reliable than the upstream 02's. 02's can lie.
The P0158 is telling the PCM that the heater circuit on the down stream has a high voltage but it sees that the upstream is working. You reported the trims are good on bank 2.
I only addressed your questions not how to fix this. If someone else has a better answer or finds my reply in error, I hope you will post in.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
"The P0158 is telling the PCM that the heater circuit on the down stream has a high voltage but it sees that the upstream is working. You reported the trims are good on bank 2."
I might be misunderstanding, but I thought P0158 was related to the sensor reading a rich condition in the exhaust stream, not anything heater element-related.
I have an entry level Autel, model AL519 . In addition to displaying PID values, it can also can graph them, though only individually. It also has Mode 6 ability, which has been helpful.
I have been looking to upgrade, though, and I've noticed FORScan seems to be pretty popular on this forum. I've a little unsure what dongle would be best to go with it in that regard, however.
Forscan won't help you on this Jeep, unfortunately. I have an AL519 as well. It'll show us Global O2 voltage PIDs, but not the true sensor voltage readings. Chrysler/Dodge/Jeep/Ram products use a 2.5V bias on their sensor ground circuits that cause the signal voltage to read 5V with the sensor electrically open (or with the sensor cold). But that may not be a huge handicap.
Because the freeze frame indicated the code set relatively quickly into an ignition cycle (64 seconds), I'm gonna guess that this isn't an intermittent problem. The flow chart Monde posted isn't terrible. :silly: Check that the sensor signal circuit isn't shorted to voltage, check that the return circuit isn't shorted to voltage, then short the signal and return together. If the signal now shows 2.3 - 2.7V (or 0V on your AL519), then the sensor has failed.
I think I know the possible reason for the code P0158. Due to a 0430 code (below threshold bank 2) on the vehicle, the signal wire going to the harness side of B2S2 O2 was disconnected and replaced with a jumper wire bonded to the signal wire on B1S2. This was done in an attempt to fool the PCM into thinking bank 2 cat was still functioning when in actuality it wasn't. I can't wrap my head around the exact reason for the P0158 the code, but I imagine it could be from the combination of a slightly richer fuel trim on that side along with the info the PCM is getting on B2S1.
Just to satisfy my own curiousity about the closed loop fault, I thought I might swap upstreams to see if it jumps to the other side. If it doesn't, I guess it would at least verify the upstream on bank 2 wasn't the reason.
To answer your questions, yes, I have a volt meter, scannerjohn. It also has a min-max capture ability also, in case that might be useful. I can take some pics of those graphs my dinky meter gives me- if you still think that'll be useful- but they'll probably be pretty crude compared to what you're used to seeing.
Guess that answers the question of whether the Jeep had prior problems and or repairs.
You'll have to restore the wiring integrity and replace that cat before you can rely on any readings.
Upstream and downstream O2's function differently and report different signals to the PCM. We can discuss that unless you already know. Also Chrysler uses bias voltages on signal and ground wires. Because of this, it's a must to use OEM 02 sensors. NTK. After market sensors such as Bosch don't work correctly.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
I think I know the possible reason for the code P0158. Due to a 0430 code (below threshold bank 2) on the vehicle, the signal wire going to the harness side of B2S2 O2 was disconnected and replaced with a jumper wire bonded to the signal wire on B1S2. This was done in an attempt to fool the PCM into thinking bank 2 cat was still functioning when in actuality it wasn't. I can't wrap my head around the exact reason for the P0158 the code, but I imagine it could be from the combination of a slightly richer fuel trim on that side along with the info the PCM is getting on B2S1.
This is much more likely to be your problem, IMO.
If you cut/disconnected the B2S2 signal wire and ran a jumper, then it's very likely that the jumper has an open or high resistance. That'd cause the B2S2 signal voltage to stay high at all times. Boom, P0158.
I'd suggest putting the B2S2 wiring back to stock, clear your codes and see what comes back. If P0158 returns, you've still got problems. If P0430 returns, either find a different way to defeat the cat monitor, or live with it. Or, replace the cat.
"Upstream and downstream O2's function differently and report different signals to the PCM. We can discuss that unless you already know. Also Chrysler uses bias voltages on signal and ground wires. Because of this, it's a must to use OEM 02 sensors. NTK. After market sensors such as Bosch don't work correctly"
Thanks in part to ScannerDanners vids, I have a decent idea on how the downstream waveforms differ from the upstreams, at least when the cat is working as it should. I'm aware of the need for OEMs on this rig and there are NTKs all around.
"If you cut/disconnected the B2S2 signal wire and ran a jumper, then it's very likely that the jumper has an open or high resistance. That'd cause the B2S2 signal voltage to stay high at all times. Boom, P0158"
Could I confirm this possibly by comparing both bank 1 & 2 rear O2 output voltages on my scanner or will the bias Chrysler uses not make that possible?
Haven't gotten around to playing with it yet. Inspection is up the end of next month, so I gotta get it down to at least one incomplete by then otherwise I'll be pulling my hair out. .
I have an AL519 as well. It'll show us Global O2 voltage PIDs, but not the true sensor voltage readings. Chrysler/Dodge/Jeep/Ram products use a 2.5V bias on their sensor ground circuits that cause the signal voltage to read 5V with the sensor electrically open (or with the sensor cold). But that may not be a huge handicap.
