2002 Liberty Engine Light Warning

[peterb]

Hi I'm new to the forum, so I hope I'm not repeating this problem. My 2002 Liberty with 282,000Km(169K miles) had an engine light warning two weeks ago. I had my mechanic put the diagnostic tester, and it came up with error code P0240, problem with the left mini cat. I had it replaced, the original was clogged up quite a bit. Left the shop, the vehicle seemed to run ok, normal power, about half hour later engine light comes on again. Back to the shop, now error code is P0138, the problem is the left bank upsteam sensor. My mistake was not replacing it before the new mini cat was installed. The new cat has to be removed to install the new sensor, so I decided to replace the right side mini cat and upstream sensor as well, before it becomes a problem sooner then later. For a few days now the engine has been running rough, as if it's misfirring.
I'll wait and see if the problem is resolved when the new sensors are installed. Are the upstream and downstream sensors identical? Also, if by mistake the mechanic reversed the sensors when he changed the cat, could this cause the problem with loss of power and rough idling?

 

[SteelHeadz]

The Part # for the Upstream and Downstream O2 sensors are different from each other, meaning , they might look identical but the connector tab locator are in different position so they can't be interchanged.. My advise, if you replace an Upstream O2 sensor, Replace the downstream as well specially from a catalytic conv. failure.. It's also a good idea to RESET the adaptives on the PCM so that it will relearn with a new set of O2 sensors and give you a better performance and fuel economy.. this is based on a 3.7 liter which i'm hoping is what's in question here as oppose to a 2.4 liter.. I hope this helps you.

 

[peterb]

SteelHeadz, thanks for info. How do you reset the adaptives for the pcm? Do you reset with an ODB2? Also, the rough idling, I learned is caused by poor or no spark on cylinder #2, according to ODB2 error code P0302. This could be a bad plug, ignition coil or wire, or combo of the later. Just murphy's law I guess that this problem occurs at this time.

 

[SteelHeadz]

SteelHeadz, thanks for info. How do you reset the adaptives for the pcm? Do you reset with an ODB2? Also, the rough idling, I learned is caused by poor or no spark on cylinder #2, according to ODB2 error code P0302. This could be a bad plug, ignition coil or wire, or combo of the later. Just murphy's law I guess that this problem occurs at this time.

I don't know how to perform a reset with a Generic scantool. With the use of Chryslers scantool, Starscan or Starmobile, there is ECU reset on the menu. if you have this on your scantool it should do the same thing... The P0302 could be one of the ones you mentioned, However, if it's a dead misfire on that cylinder, i suggest that you remove the valve cover and check the rocker arm..I've seen this on the 3.7 and 4.7 where the rocker arm has slipped off it's cradle and created a Misfire.. Start by swapping the coil on a cyliinder thats not misfiring and see if it follows..if not, do the same procedure with the spark plug.. if you still have a misfire, check the injector and wiring.

 

[peterb]

Again thanks for info, will have mechanic replace the right mini cat and o2 sensors tomorrow, and as well try to resolve misfiring problem.

 

[peterb]

Well, the problems continue, after replacing both mini cats and upstream o2 sensors, I was expecting a better fuel mileage and normal power, this didn't happen. Also, the misfire problem is still showing on the ODB code reader despite having swapped coils and replaced #2 plug. Decided to leave at the dealer, the tech is reading the misfire code and sensor code. Don't understand why he's getting a sensor code. I could only see the P0302 on my ODB box. I told him what I had replaced, and he will hopefully track down and repair the problems.
I will update on results.

 

[SteelHeadz]

Check your PM for some info.

 

[peterb]

How do you check power module for more info? As I mentioned yesterday, the vehicle was at the dealer and tech is seeing a voltage on one of the connector pins with sensor disconnected. This could be a short somewhere between the PCM and connector. With no sensor connected the only wire that would show 12volts, is the heater element line, which might indicate a faulty relay. This line should only have voltage on start up when engine is cold, open loop mode. In closed loop, the sensor does not need this voltage. At least the engine misfire problem has been corrected.

 

[SteelHeadz]

How do you check power module for more info? .

Sorry, PM meaning Private Message.. look at the Welcome bar under the Jeepz logo and click on the private message..
Anyways, is the problem fixed?

 

[peterb]

Not yet, will know by tomorrow. Thanks for clarifying "PM', sort of new to forum abreviations.

 

[peterb]

Ok, I'm starting to hate oxygen sensors. The problem with the left bank upstream O2 sensor was caused by dirt or gease on the connector contacts. Now another sensor code has popped up "P0158', this is a heater circuit high voltage on the right side downstream sensor. A new unit has been ordered and when installed, will I hope mean the end of sensor problems for a while.

 

[peterb]

Here's the update on the sensor issue. The P0138 problem was fixed for now, the tech attributed the fault to gease on the coonectors and wires. The latest code is a P0158, the right side dowstream sensor, dealer ordered a new one and the tech made a mistake and replaced the dowstream on the leftside(Driver). He said he tried to remove the right side DS sensor when he was trouble shooting the P0138 fault, but felt it was seized to the cat, and feared breaking the thing. That's BS, that sensor was easily removed from the original cat, and was installed on the new cat with normal torque. Going back tomorrow, and will insist this problem be reolved at no more cost, since I have already paid for a new sensor and labor charge. Bottom line, it's hard to find competent technical people, even at dealers.