2006 4.0 Flashing CEL at Idle

[basaraski]

Hey guys, first time poster here. Bought my '06 4.0 (auto trans) a little over a year ago. Had a lit CEL for a faulty o2 sensor when I bought it.

Recently the CEL has begun flashing, but only at idle once up to operating temp (wont flash at idle from cold start). It also starts to smell like its running very rich, which is 100% the case from the DTC's its showing.

Only recently did I have my first misfire from this. It was after a long wait at a red light. Once I began driving it sputtered some, but then was fine right after. It also seems my fuel mileage is terrible, as to be expected. Other than that, when driving at normal speed she seems totally fine. Idle is when it gets rough and CEL flashes/rich smell.

Just want some insight on what to attack on this first? all o2 sensors? Are my pre-cats bad? (This is a cali - 4 o2 sensor TJ) Camshaft sensor, coolant temp sensor, or even the dreaded failing PCM? This is my first Jeep so also learning all of this as I go.

One more note, I may have some type of ground issue, as months ago she wouldn't start, but once cleaning the ground terminal it was fine, but randomly the ground seems like it disconnects, as my radio resets, and the CEL goes away for a bit.

Here are the codes its showing.

P0138 - O2 Sensor Circuit High - Bank 1, Sensor 2
P0301 - Cylinder 1 Misfire
P0171 - System too lean bank 1
P0172 - System too Rich bank 1
P0174 - System too lean Bank 2
P0344 - Camshaft position sensor A circuit intermittent - Bank 1 or single sensor

Any help is greatly appreciated.

 

[ItchyDong]

The flashing CEL is the misfire.

If you want to throw a Hail Mary, remove and clean G105 at right rear of engine block. The PCM uses this ground which could explain the O2 codes and computer control ground for an intermittent injector. And the cam shaft sensor also uses this ground.

I could nit pick this all day, but it’s quick and easy. If it doesn’t resolve the issue, further troubleshooting would be required.

I’ll be happy to help but you’ll need a test light, multimeter, and scan tool with live data. I won’t waste my time typing all that up unless you’re interested.

 

[JKP]

The flashing CEL indicates a misfire that is dumping raw fuel into the cats. It will destroy the pre cats eventually.

Check the O2 wiring.

How are the spark plugs?

Check the OPDA wiring where it goes over the dipstick. Is the OPDA the OEM one? Has it been checked for wear?

Check the battery cables and grounds for corrosion.

If you have hard shifting, engine cutting, out, O2 heater codes, gauges dropping out, those indicate the PCM.

 

[basaraski]

The flashing CEL indicates a misfire that is dumping raw fuel into the cats. It will destroy the pre cats eventually.

Check the O2 wiring.

How are the spark plugs?

Check the OPDA wiring where it goes over the dipstick. Is the OPDA the OEM one? Has it been checked for wear?

Check the battery cables and grounds for corrosion.

If you have hard shifting, engine cutting, out, O2 heater codes, gauges dropping out, those indicate the PCM.

Gonna check all wiring today. Plus the ground at G105. Not sure on the OPDA, I got the Jeep about a year ago.

No hard shifting, no engine cut out, or gauges dropping out at all. Outside of the idle, it runs/starts completely normal.

 

[basaraski]

The flashing CEL is the misfire.

If you want to throw a Hail Mary, remove and clean G105 at right rear of engine block. The PCM uses this ground which could explain the O2 codes and computer control ground for an intermittent injector. And the cam shaft sensor also uses this ground.

I could nit pick this all day, but it’s quick and easy. If it doesn’t resolve the issue, further troubleshooting would be required.

I’ll be happy to help but you’ll need a test light, multimeter, and scan tool with live data. I won’t waste my time typing all that up unless you’re interested.

I have a sneaking suspicion the ground at G105 could be the culprit, have yet to take a look at it. That could cause all these issues? At least I hope it's just that.

Not sure my cheap code reader has live data, but I'll check.

 

[JKP]

If the OPDA says LDI on it, it is OEM. They are known for becoming hard to turn, seizing.

 

[basaraski]

If the OPDA says LDI on it, it is OEM. They are known for becoming hard to turn, seizing.

Okay, I will take a look at this as well.

Was also just reminded this already has a new PCM in it. So I guess that's a good thing? In theory could also be the problem lol

 

[JKP]

It's good if it says wranglerfix.

 

[basaraski]

It's good if it says wranglerfix.

It does. Wohoo

 

[basaraski]

UPDATE:

Was just reminded of the work done prior to my purchase of this TJ

New PCM (Wrangler Fix)
All new o2's (CEL remained)
New Transmission
New Radiator
New Water Pump

 

[JKP]

Definitely look into your wiring, many times it gets nicked, crushed during transmission or engine removal, installation.

 

[basaraski]

The flashing CEL is the misfire.

If you want to throw a Hail Mary, remove and clean G105 at right rear of engine block. The PCM uses this ground which could explain the O2 codes and computer control ground for an intermittent injector. And the cam shaft sensor also uses this ground.

I could nit pick this all day, but it’s quick and easy. If it doesn’t resolve the issue, further troubleshooting would be required.

I’ll be happy to help but you’ll need a test light, multimeter, and scan tool with live data. I won’t waste my time typing all that up unless you’re interested.

So i cleaned G105. As it was pretty much fully covered in oil. Test drove 10 mins and no CEL. Didnt even idle rough at operating temp, nor smell like its running rich. Although I still think Bank 1 sensor 2 is shot. At least i think that's what the limited live data shows? Not getting any voltage to it. Bad sensor or wiring?

 

[ItchyDong]

With the key in the run position and engine off, unplug the sensor while watching live data and see if O2B1S2 Volts jumps to 5 volts.

 

[basaraski]

With the key in the run position and engine off, unplug the sensor while watching live data and see if O2B1S2 Volts jumps to 5 volts.

Will do. Just did another test drive. 30 mins this time. No issues at all. No CEL. No rough idle. Did check live data again, and now that B1S2 has voltage but constant above 1v compared to the ~.7v of B1S1.

 

[ItchyDong]

Do the unplug test when the sensor is cold or it won’t show 5 volts. But, if the data you took pictures of is LIVE data and not freeze frame data, then it’s getting stuck both rich and lean positions. Replace the sensor.

 

[basaraski]

Do the unplug test when the sensor is cold or it won’t show 5 volts. But, if the data you took pictures of is LIVE data and not freeze frame data, then it’s getting stuck both rich and lean positions. Replace the sensor.

Yes it was LIVE. Already have a new sensor coming in Thurs

 

[ItchyDong]

Scratch that. The unplug test won’t read 5 volts. I’m thinking of old non-computer control o2 heater circuits. Yours is computer controlled and that won’t work. There’s ways to test the sensor forcing rich (carb cleaner in intake) and lean conditions (creating vacuum leak) while monitoring signal voltages, but honestly being that it’s stuck in both rich and lean positions, it’s a really good chance it’s a sensor and not a circuit issue.

Make sure you get a good brand. There’s a ton of debate but NTK is usually the recommended. Our jeeps are REAL picky about their O2’s.

 

[basaraski]

Scratch that. The unplug test won’t read 5 volts. I’m thinking of old non-computer control o2 heater circuits. Yours is computer controlled and that won’t work. There’s ways to test the sensor forcing rich (carb cleaner in intake) and lean conditions (creating vacuum leak) while monitoring signal voltages, but honestly being that it’s stuck in both rich and lean positions, it’s a really good chance it’s a sensor and not a circuit issue.

Make sure you get a good brand. There’s a ton of debate but NTK is usually the recommended. Our jeeps are REAL picky about their O2’s.

Yep ordered a NTK o2 yesterday.

Shows as a pending DTC, but hasn't triggered a CEL yet. Still very relieved all the other issues were bad ground connection. Knock on wood at least. Hopefully running it a bit in that state didnt screw my pre-cats

 

[Jakes-2004-TJ]

Hey guys, first time poster here. Bought my '06 4.0 (auto trans) a little over a year ago. Had a lit CEL for a faulty o2 sensor when I bought it.

Recently the CEL has begun flashing, but only at idle once up to operating temp (wont flash at idle from cold start). It also starts to smell like its running very rich, which is 100% the case from the DTC's its showing.

Only recently did I have my first misfire from this. It was after a long wait at a red light. Once I began driving it sputtered some, but then was fine right after. It also seems my fuel mileage is terrible, as to be expected. Other than that, when driving at normal speed she seems totally fine. Idle is when it gets rough and CEL flashes/rich smell.

Just want some insight on what to attack on this first? all o2 sensors? Are my pre-cats bad? (This is a cali - 4 o2 sensor TJ) Camshaft sensor, coolant temp sensor, or even the dreaded failing PCM? This is my first Jeep so also learning all of this as I go.

One more note, I may have some type of ground issue, as months ago she wouldn't start, but once cleaning the ground terminal it was fine, but randomly the ground seems like it disconnects, as my radio resets, and the CEL goes away for a bit.

Here are the codes its showing.

P0138 - O2 Sensor Circuit High - Bank 1, Sensor 2
P0301 - Cylinder 1 Misfire
P0171 - System too lean bank 1
P0172 - System too Rich bank 1
P0174 - System too lean Bank 2
P0344 - Camshaft position sensor A circuit intermittent - Bank 1 or single sensor

Any help is greatly appreciated.

I have a 2004 TJ with 4.0L with a manual 5 speed tranny, it has about 170k miles on it. Symptom's: initial problem was random CEL (Check Engine Light), usually steady, but later would flash at times with jerky acceleration. Code reader gave cylinder 1 misfire that later became cylinder 5 misfire. During acceleration, engine would backfire into the breather, so I thought it was a gas/air mix ratio problem. New spark plugs had no effect on fixing the problem. With the engine running, I could hear the fuel injectors clicking by placing a long screwdriver on each injector and the handle on my ear. I disconnected and did a resistance test on all of the fuel injectors, all of them read 13.7 ohms. I saw a message that the IACV (Idle Air Control Valve) can cause all these problems, especially if stuck open or stuck closed. I removed the IACV and found lots of carbon build-up. With the engine off, I pushed the throttle butterfly fully open and looked inside the intake, it was also caked with carbon. GUM-OUT cleaner was sprayed heavily throughout the intake and IACV passages, I also used a toothbrush to scrub some areas. I disconnected the battery (for about an hour) while I installed a new IACV. Once everything was back together, I started the engine and the CEL remained off, went on a test drive and the CEL remained off. As I understand it, disconnecting the battery resets the ECM (Engine Control Module) so it has to learn where to set the new IACV during start / idle / acceleration and steady driving. It appears the IACV is a jack-screw type valve, a dual direction electric motor extends or retracts the IACV plunger, which varies the gas / air mix ratio based on engine temperature, but adjusts for power demands too.

 

[Torque710]

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