Douglas Moore

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

AZJKU2017

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

gfe jeep

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

Mr.T

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.

gfe jeep

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!

Jim553

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?

Mr.T

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?

Mr.T

Here's a schematic of O2 sensor 1/1 for reference, the others are similar - just different connectors/pins.

Jim553

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.

Jim553

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?