P0031 after replacing all 4 O2 sensors, EGR, plugs/wires/coil
 

Hey guys, first post. Sorry to ask for help before contributing anything, but I’m kind of lost. I replaced all four O2 sensors, EGR valve, plugs/wires/coil today on my wife’s 08 Unlimited Sahara to battle a plethora of codes, including multiple 02 sensor faults and a random misfire issue. Jeep runs amazingly well now, but I still have a P0031 code. I’ve looked pretty hard on google, YouTube, etc, but cannot find anything JK specific regarding a fix or troubleshooting procedure. I’d really appreciate any help y’all can give, I’m really struggling here. I’m back at it tomorrow doing ball joints and some other maintenance items so I’ll be able to run down any rabbit holes y’all can suggest. Thanks!

doug

1/1 o2 sensor heater control circuit... Make sure you have no power to o2 sensor heater circuit with key off, if you do you will burn out o2 sensor. Basically you have a wiring issue from pcm to 1/1 o2 sensor (circuit k99 br/lg wire cavity 1) or you have a bad ground from o2 to ground (z906 black wire cavity 2).. Check for power with command heater on to k99, check ground at cavity 2... If this checks out you have a defect o2

Is it possible
 

Hi
I had all of these codes show up at on time:
P0031 P0037 P0051 P0057

Could all four actually go out at the same time? I have a 2008 JK Sahara

Thanks George

Hi George, all those are O2 heater circuit low codes -- Strange, even more significant is that replacing all four O2 sensors cleared all but one. Here's the potential causes from the manual, the difference between codes is which O2 sensor. P0031 is 1/1 (passenger upstream).

It looks like a current limited circuit in the sense that a ground will sink the voltage to near zero and set the circuit low code. Conversely, if the heater is an open circuit the voltage goes high and sets the circuit high code. The 70F O2 heater resistance is supposed to be 2 to 30 ohms, the heater + is pin 1, the - (ground) is pin 2 of the connector.

Thanks Mr T
 

Thanks for the information. This was my original issue then other codes and problems were found. I eliminated all except these four. I also read about 02 eliminators but would do that as a last resort. I think some of my problems were a caused by a spike in voltage from the alternator. I have determined the PCM is working, repaired some grounds (one was broken that went to the engine block). During this time I replaced the ERG, and spark plugs and wires. I have a Crankshaft Position sensor on order for rough idle. I'll check the wires that go into the )2 sensor plugs next.

I'll see if I can find hows this is operating!

I’m having an O2 sensor issue. All 4 sensors read high. With the sensor disconnected I get a ground on all 4 wires going to the ECM. I disconnect the orange connector and the grounds go away. I read that an open would cause a high ckt indication. Does that mean I have an open between the connector and sensors? Would I get a high ckt indication if I left the 1-1 sensor disconnected? I have replaced the EGR valve, and PCM, I had an issue where the Jeep wouldn’t start but after running a ground wire from the battery to the engine ground it starts fine. What should I do now?

What stands out is that all 4 O2 sensors read high -- I'm presuming you are reading the sensor output on an an OBD2 scan tool, correct? They do not all go through the same connectors, the common single failure sounds like the PCM. Maybe it's 4 bad (incompatible) O2 sensors, or some strange and unlikely combination of problems affecting all 4 sensors.

Regarding what does an O2 sensor reading do with a disconnected sensor, I believe it will read high on a scan tool.

Is this possibly related to replacing all the O2 sensors? What orange connector are you referring too, and which side of the connector is being tested? What method are you using to determine that all 4 wires from each O2 connector to the PCM are showing they are grounded?

:beer:

O2 sensor 1/1 schematic
 

Here's a schematic of O2 sensor 1/1 for reference, the others are similar - just different connectors/pins.
https://cimg4.ibsrv.net/gimg/www.jk-...0aa3cf25d8.jpg

The sensors go through the two middle connectors on the PCM right? The orange connect is the second one counting from the drivers side of the vehicle. Back info I was not able to start the Jeep with out disconnecting and reconnecting the orange connector. I fixed this by running a ground from the battery to the engine ground. The sensors were working fine then 1-1 went high, replaced that twice, and a cracked exhaust manifold, Then 2-2 went high, a week went by and all sensors read high. I read the sensors and they all have 2 to 8 ohms across the heaters. When I read the wires going to the pcm all the wires had either .8 to 0 ohms to ground. I replaced the PCM. Same issue. I started getting misfires if 1-1 was connected. So 1-1 is now disconnected. I thought I had a ground issue but then read that you get a high indication if there is an open. I do not know what I should read went testing the PCM connectors. I figure I should try reading the PCM connector to the sensor connector however I’m not sure what pin goes to what. I don’t want to waste money on a harness if that’s not the issue.

I appreciate the schematic, I have a question. If I’m looking at this right the heater ckt and sensor ckt are separate right? If that’s the case then when they say that an open would give you a high indication are they talking about on the signal side or heater side?

Sorry another question, the s133. What does that mean? Is that just a connection point or am I mistaken?

The pin and connector for 1/1 are in the scheme above (post 8). With 1/1 disconnected does it read high on a scan tool?
:cheers:

The S prefix is a splice and G is a ground. :cheers:

Interesting question! Connector disconnected, as mentioned earlier i believe it should read high. Sensor circuit open, same -- floating high. Now for an open heater circuit, which will set a separate DTC for heater circuit high, I believe it will be something above 2.52 volts based on the criteria for P0131 O2 sensor circuit low:

Yes with 1-1 disconnected I still get a high with the scan tool. I do not know why when it is connected I get misfires. I going to find a schema for all 4 sensors, maybe there is a common connection point or route the harness takes that could of opened?

Mr. T I seem to of missed some of your questions. I’m using a fluke meter to take all my readings. I have a scan tool to read the fault codes and reset them. That’s about the extent of its capabilities. Would you know where I could get a full pin out for the second connector on the PCM?

I took reading on the C2 connector. Between c18 and C31 I had 0 ohms. Both C18 and C31 go to the same pin on the connector between the harness and sensor.

never experienced it. but this is a really very interesting discussionhttps://juragan.club/assets/8/o.png

If I understand, C2/18 and C2/31 are shorted, measured at C2 toward the 1/1 O2 sensor (not the PCM). The way I'm denoting this is Connector/Pin, so C2/18 is Connector C2 pin 18. This is all per the O2 1/1 schematic above.

But here's where I'm confused, C2/18 goes to pin1 at the 1/1 O2 sensor connector (heater +) and C2/31 goes to pin 4 at the O2 sensor connector (O2 1/1 signal). With the sensor disconnected (or connected), the resistance should be infinity between these points regardless of whether measuring at C2 or the O2 sensor connector (and I'd do it both ways). If it's actually shorted, the wiring is bad -- very uncommon but possible if critters are munching on them.

You could really benefit from getting some type of scan tool or software that can read values from the PCM. If you have a laptop, the Appcar DiagFCA software with an OBDLink MX+ bluetooth adapter (includes OBDwiz graphing software) is very capable. There's others too, I did a review in a recent post you can search for. Knowing how to use a meter is great, but often it takes knowing what the PCM is actually seeing, and starting there is a lot easier/faster.

This only matters if you're doing key-on voltage measurements, but Chrysler/Jeep usually has a bias voltage on the O2 sensors. With a 2.5 volt bias -- Measure 3.0V with a meter and OBD2 software like HPTuners will show 0.5 for sensor volts from the PCM, but there could be a scanner tool or software that include the bias and display the raw 3.0V.

On of my favorite methods using a voltmeter is to use a sewing needle to pierce the insulation, and attach the meter lead to the needle for in-circuit measurement. When finished smear some silicone sealer where the needle was.

Haven't found a pin-out the C2 connector, will take another look.

:cheers:

PCM C2 pin-out
 

Found it, PCM C2 pin-out:
https://cimg2.ibsrv.net/gimg/www.jk-...8e5f29b702.jpg

DTC's
 

Forgot to ask about DTC's. With everything connected, what are the codes? Trying to make sense of the meter measurements with what failures the PCM has detected.

:cheers:

Splice S133
 

Here's the scheme for the 2/1 O2 sensor. Note that the signal return (likely with the 2.5V pull-up bias) is the exact same pin (C2/32) as the 1/1 sensor -- via the splice S133, wire K902, and connector C2/32.

Odd how they make you look at both schemes to figure out what that splice is for. This little detail may figure prominently when ohming out the wiring.
:cheers:

https://cimg8.ibsrv.net/gimg/www.jk-...2632785a55.jpg

I reconnected everything and ran the Jeep for about 30 miles. The codes I have is PO155, 0032, 0052, and 0155 again I had a P0300 but that reset.

I looked up the numbering for the black orange connector. I apologize I may of been reading the wrong points because the reading I have now are different from this morning. C32 is OL, 18 is 0 Ohms to ground.
Between 18 and 32 OL. 18 and 32 wring out to separate pins on the O2 sensor connector.

I reconnected everything and ran the Jeep for about 30 miles. The codes I have is PO155, 0032, 0052, and 0155 again I had a P0300 but that reset.

I looked up the numbering for the black orange connector. I apologize I may of been reading the wrong points because the reading I have now are different from this morning. C32 is OL, 18 is 0 Ohms to ground.
Between 18 and 32 OL. 18 and 32 wring out to separate pins on the O2 sensor connector.

I don’t know if just disconnecting the sensors and reconnecting them changed anything but now from the codes it looks like it is just the 1-1 and 2-1 sensors that are having and issue with the heater side. Im looking into a better scanner or a cheap computer.

G104 ground
 

Look for the ground G104 in the schematic and see if it has a high resistance -- anything over a couple ohms is too high, and it could be an intermittent bad connection. This single item would cause all the codes listed.

More later, but figured you might be working on it now. :cheers:

Have a feeling you're getting close to a solution. More pin-outs...
https://cimg4.ibsrv.net/gimg/www.jk-...8005d24b10.jpg


As mentioned prior, still have a strong suspicion that G104 has high resistance. Note how both 1/1 and 2/1 sensors share this ground, and a high resistance ground G104 will cause all the codes mentioned. Also, the heater elements are supposed to have 3-30 ohms at 70F temperature when checked with a meter.

Here the code definitions:

P0032 O2 1/1 heater ckt high
P0052 O2 2/1 heater ckt high
Basically these codes mean that the PCM pin feeding the relevant O2 heater circuit has higher voltage than expected -- for example there isn't ant current draw from the heater element within the O2 sensor.
P0135 O2 1/1 heater ckt performance
P0155 O2 2/1 heater ckt performance

More on G104
 

Looks like G104 is one of the infamous engine grounds (O2 heaters, EGR, A/C clutch), the other is G101 (back to the battery, sized for the starter motor). All the O2 heater ckts are tied to it. It is located on the passenger side of the block, toward the rear, near the knock sensor. It is across from the cat. Taking it off completely is a big job, but I think a thin open-end wrench can be used to tighten it. Maybe grind a wrench thinner to get in there -- It's a double nut affair if I remember correctly, the outer holding the heat shield and the inner holding the ring lugs to the block.

Don't know how all the devices that use G104 get connected. Could be the wiring between G104 and the 1/1 and 2/1 sensors connector pin 2 heater ground is open/high resistance. However, it's interesting that the 2/1 and 2/2 O2 sensors don't have the heater high codes (yet), but it sounds like they did prior -- If so that would be even more convincing that G104 is the issue.

Here's where G104 and G101 are located... It's bedtime here, good luck tomorrow :cheers:

https://cimg4.ibsrv.net/gimg/www.jk-...5976191926.jpg

I appreciate all the help Mr. T, I traced the wiring out to the same ground lug I ran the negative battery to. Pretty much exactly like you said and in the picture. I bent the heat shield and removed all three ground connectors cleaned them up re-installed everything, erased the codes and still had the issue. I reterminated the O2 wires and reconnected everything, cleared the codes, still had the same issue. I pulled the terminal with O2 sensors wires and ran it to the ground terminal Where the hood is grounded. Cleared the codes and no engine light.
Could it of been the ground wire I ran from the battery that was causing the issue? I don’t see how though.

Again I appreciate all the help and you taking the time to look things up and impart some knowledge to me.

Good troubleshooting move by wiring the O2 heater grounds to where the hood is grounded. You've proven (the original) G104 was a bad connection back to battery neg, likely an intermittent problem that won't easily show up with ohm-ing it. BTW- one way to ohm suspect intermittent wiring is wiggling the wires, especially at connection points, while measuring resistance on the lowest scale.

For proper operation, G104 has to make it all the way back to the battery negative with a solid low resistance connection, and since the connection at the block where you bent the heat shield for access has been cleaned and tightened -- I think it might be that the G101 large wire on the same bolt going from the engine block (you already cleaned that end) to the battery neg has a bad connection. It could be a loose crimp, corrosion, or even the wires have a break inside the insulation (from vibration maybe) -- Check the top end first since it's easier. Some of the hardest problems to troubleshoot are intermittent wiring, but you have really narrowed it down to just that section of wiring (essentially G101) replaced to get it functioning with no codes.

Regarding the extra ground wire added earlier: Where exactly is the added ground wire connected at both ends? This wire should have provided another parallel path from the engine block to battery neg, keeping this issue from happening even if the G101 wire is bad. It doesn't quite make sense (yet) why the starting issue was apparently resolved by adding this redundant ground but the O2 sensor heaters still can't get a good path back to battery neg.

Hope this helps narrow it down further! :cheers:

I was getting the infamous click when you tried to start the vehicle. I knew that it had to do something with C2 because I would pull that off and reattach it and the Jeep would start like normal.

the secondary ground is going straight from the negative side of the battery to the engine ground. I figured that should of solved all the issues. Though I did cut about 3 inches off the O2 sensor wiring to be able to reroute it to the hood. So like you said there might of been a break close to the terminal lug that was removed during my rewiring of the ground.

i really appreciate the help I’ve been working on that off an on for that last month and with your help fixed it in two days. Really appreciate it!

Your welcome :cheers: