2002 Jeep Grand Cheerokee Laredo hesitate/jerking + multiple CEL codes

Question

I have a 2002 Jeep Grand Cheerokee Laredo 4.0. I don't know much about cars, and recently had bought this Jeep off of a private owner that had said it had no problems but now after owning it for 2 1/2 months it has PROBLEMS! And it's becoming a bit stressful!

I've taken it to 2 different shops but both shops have given me only predictions on what is wrong with it and I have no idea which mechanic to believe because they are both giving me different answers. So let me explain what it is doing and hopefully someone here can help me figure this out to get it repaired.

The first thing that happened was the check engine light came on, so I had it tested & was told I needed spark plugs, so I had those replaced. The Jeep was fine but a week later the check engine light came back on, so I took it back in & was told my oxygen sensors need to be replaced. I'm working on getting those, in the meantime a few day go by and the Jeep begins to hesitate and jerk at stops and when I leave from being parked.

Now I don't know what is wrong with this??? Can someone help explain this? I am also now experiencing overheating of my engine and ticking. Not knocking but ticking. I have checked my radiator & have discovered the previous owner must of put stop leak in the radiator at some point according to the mechanics so now I was told that needs to me completely flushed out of the system & needs a new radiator because the radiator looks to have been patched and may not be holding. Any answers on all of the please?

EDIT: The codes I had printed out were P0135 02 Heater Circuit (Bank 1, Sensor1), P0141 Oxygen Sensor Fault, Right Side, Post Catalyst, P0155 Oxygen Sensor Fault, Left Side, Before Catalyst, P0161 HO2S-22 (Bank 2 Sensor2) Heater Curcuit Malfunction. Then it said Definition: Code P0135 indicates a fault in the bank 1, Sensor 1 O2 Heater electrical circuit for a predetermined period of time.

Answer 1

As Moab pointed out, your issues are very "generic", meaning there's a number of things that could be causing them. Here's what you do:

1. When the check engine light comes on, it means the computer has found something wrong with something and has stored a trouble code in it's memory to tell you what it found. Most car parts stores will read these codes for you for free, no need to go to a shop and pay for this.
2. Your first issue was the check engine light came on and somebody changed your spark plugs because of it. While there is no trouble code that says you need to replace spark plugs, there are a few generic trouble codes where the first and most likely and less expensive "guess" is bad spark plugs. Call that mechanic or shop and ask them what the trouble code was that time, because the Jeep started having issues again a short time later. It could be a different problem, or it could be the same problem that came back.
3. Your second issue was a week later where the check engine light came back on and you were told to have the O2 sensor replaced. There is a trouble code for a bad O2 sensor when it goes completely bad and it gives the computer some readings that are "out of range." However, most of the time (in my experience), when O2 sensors cause problems is because they are reading wrong or reading too slowly, and there isn't a trouble code specific for that. Call that shop and ask what the trouble code was that time.
4. Your third issue is the Jeep jerking and hesitating at stops and when leaving a parking spot. Engine trouble that occurs only at low-speeds is likely to be the Idle Air Control valve. It may need replacing, or it may simply need a cleaning, or maybe the electrical connection to it is loose.
5. Because of the age of the Jeep, it is normal to get a lot of nagging little issues due to neglected maintenance from previous owners. None of these issues sound too expensive, just get us the trouble codes and we'll guide you to a diagnostic. Most mechanics just like "throwing parts" at a vehicle until the problem or the client disappears. A lot of the simple repairs only need basic tools and basic skills, so if you have a mechanically-inclined friend, he or she may do this for beer or a warm meal. Labour on auto repairs usually ranges between half and 2/3 of the repair bill, parts are cheap.

Answer 2

Regarding the O2 sensor codes. Check fuse 16 in the under hood fuse box. It's likely to be blown. The only point all four sensors have in common is the fuse. If the fuse tests good I'd pull up the fuse box and find the two wires that go to each O2 heater circuit. They'd be crimped together on one terminal. If that checks out then next would be the downstream relay and wiring harnesses/connectors. If the fuse is blown and blows once a new one is installed you have a short to ground on one of the wires and will need to be traced. A common rub through point on the 4.0 is around the rear portion of the valve cover. There should be a plastic piece that holds the harness away from the valve cover but sometimes it gets discarded.

Answer 3

Here's what your trouble codes mean:

• P0135: O2 sensor heater circuit (bank 1, sensor 1)
• P0141: O2 sensor heater circuit (bank 1, sensor 2)
• P0155: O2 sensor heater circuit (bank 2, sensor 1)
• P0161: O2 sensor heater circuit (bank 2, sensor 2)

It sounds like all 4 of your O2 sensors are failing for the same reason, and I find that hard to believe. What is most likely (in my opinion) is that either:

• the sensors are covered with soot that is cooked on pretty good preventing the heater circuit from operating properly
• there is damage to the wiring harness of the sensors

Option 1 is likely because of age and mileage, option 2 is only possible if all 4 sensors share the same wiring harness.

If it's option 1, you need to make sure the engine is burning cleanly, otherwise the issue will return. If it's option 2, the harness will either need to be repaired or replaced.

All this being said, bad O2 sensors will only likely cause the engine to be less fuel-efficient and pollute more. This is unlikely to cause the jerking at slow speeds you have reported. This is likely the Idle Air Control Valve as has been suggested, or something in the engine isn't running perfectly, so we are talking about:

• not enough air (inspect your air filter, they are $10 to replace)
• not enough fuel (replace your fuel filter, $15 for most cars)
• not enough spark (spark plugs are new, were they set to the proper gap? Spark plug wires/coils would be next, about $20 each and you have 6 of them)

Call the shop that replaced the spark plugs and ask them about the spark plug gap, since the jerking issue started after the new plugs. A lot of mechanics buy into "spark plugs come pre-gapped." This is BS. I always check the gap of spark plugs before putting them in, the gap is always all over the place fresh out of the box.