Bought a new Jeep-Now I have some codes to fix...

So I just bought a Jeep and it threw some codes at me on the drive home hang. After looking them up, it seems like a fair amount was wrong with it and the seller did not disclose that to me. I guess it is a good thing I have not sold my extra vehicle...

The codes are:

P0123
P0121
P0700
P0122

So, after driving the Jeep and looking up the codes, I imagine the issue has to do with the Throttle Position Sensor (TPS) and something with the transmission cry. How have you repaired these codes before? I am rather disappointed in the Jeep and pretty upset that the seller was such a piece ofuke:...

What year is this heep? What motor?

Edit: P0700 is a generic code indicating a fault has been set in the TCM. The TPS communicates with the TCM so if the TPS is dicked up bad info will be sent to the TCM, and the TCM doesn't liked to be dicked with.

If you end up changing the TPS get an OEM part from the dealer (big bux). Aftermarket ChiCom parts, like from Advance, O'reilly, and Analzone do not last long. NAPA Echlin TPS will do in a pinch.

Thank you for the reply. It is a 1998 with the 4.0 engine. So the best replacement parts are the ones from the dealer?

When I was driving it today to O'reilly's it died at the stop sign about 150 feet from my house. Then when we got onto a road at 35mph, the Jeep would not accelerate easily. I pushed on the gas and the RPMs went to 2500 then almost to 3000. Once I pushed hard and then let off the gas, it helped a little and it acted more normal. It died again when I was leaving the parking lot. When I put the Jeep from DRIVE into PARK, the RPMs go to about 1600.

Another couple of issues are:
The horn, cruise control, and door locks do not function...

As I think of more things, I will post them.

vikingxj said:

When I was driving it today to O'reilly's it died at the stop sign about 150 feet from my house. Then when we got onto a road at 35mph, the Jeep would not accelerate easily. I pushed on the gas and the RPMs went to 2500 then almost to 3000. Once I pushed hard and then let off the gas, it helped a little and it acted more normal. It died again when I was leaving the parking lot. When I put the Jeep from DRIVE into PARK, the RPMs go to about 1600.

Another couple of issues are:
The horn, cruise control, and door locks do not function...

As I think of more things, I will post them.

Click to expand...

Well, the uncontrollable engine speed sounds like the Throttle Position Sensor. If the PCM believes the throttle has been opened up, it will toss in more fuel. Let's fix this one first before going onto the others as this one makes the Heep dangerous to drive...

For the other electrical gremlins, start with looking at both sets of fuses. The set in the PDC under the hood and the set that reside in the passenger side kit panel.

Fortunately, IMO the '98 model year is the best but then, I may be a tad biased on that one...

As an aside, if this is your first XJ, tone of the best things you can do is to refresh all of the ground connections. Most here will recommend that the stock cables be replaced with upgrades (read larger wire here) and I agree with that. Chrysler did not put anything extra into the XJ.

If you want to check/clean your engine bay ground points here's some visual guidance and notes:

G100. The main battery negative (-) path to the chassis. This ground point gets corroded. The bolt is 8 mm and uses a 13 mm wrench. Remove it and flush all the rust off the fender and the wire ring terminal. Renew the bolt if required.



G101. The main battery (-) path to the engine. The engine is the ground path to circuits related to the engine and transmission for the most part, but other important circuits are grounded here (see pic). Remove and clean these ring terminals and reattach. THe nuts are 5/16' and use a 1/2" wrench.



G106. G106 has two sheet metal screws holding the ring terminals down on the left inner fender, located under the wiring looms near the PCM. Circuits grounded here are shown on the pic. Remove these screws and clean the ring terminals, remove the rust on the fender and replace the screws as required.



G102. G102 is the ground point for the Data Link Connector. It is located at the oil dipstick tube attach bracket. If you ever have trouble with a code reader or scanner not connecting, this ground may be the cause. Clean the ring terminals.



Firewall/Engine Ground. This ground was originally intended to prevent radio interferance from the ignition system. It's a bonding strap, not a cable/wire like the rest of the grounds. It goes from the firewall to left rear cylinder head bolt. It does provide an alternate ground path to the chassis however. If G100 is compromised by corrosion this ground would help provide a chassis ground, through the engine (G101). The bolt is 10 mm and uses a 15 mm wrench. Remove the bolt and remove the rust from the firewall, clean the ring terminal, and replace the bolt if required. Remove the nut that secures the other ring terminal to the cylinder head stud. Clean the ring terminal and replace the nut if required.



Clean the ring terminals with Scotch Brite pads. Flush using CRC Electroincs Cleaner. Do not use Dielectric grease on these ground points (as some would suggest).

Good luck.

THANK YOU VERY MUCH for the great photos! You must have scrubbed your Jeep down very well before those pics! I have tomorrow off so I will check out the different things you mentioned. I also have to install a windshield wiper motor on my GF's VW tomorrow...

So I installed a new TPS and it seems to idle a little better, but when I push it up over 1600rpms, and then let off the gas, it dies. When I slowly let off the gas, it idles below 1000RPMs. The check engine light is still on as well.

Any ideas given the new info? Also, the K&N filters...are they washable?
Thanks.

The fan belt came off yesterday when I was revving it up...I went to put it back on and it turns out it is about 10" too long! :huh:How did I drive it home without it overheating? This thing is weird.:doh:

No way the belt was that much to long. You sure your routing it the right way?

Ever fix your trouble codes on this one. I know its an old post, but Im getting p0122 p0123 p0700

It was the TPS that needed to be replaced. I also cleaned out the throttle body with cleaner and put it back together. Other problems that were happening were the harmonic balancer was toast and "walking" the crank in the direction of the radiator. The harmonic balancer was wobbly, hence the belt being thrown from the pulleys. Luckily it didn't walk into the timing cover. I also replaced the water pump as that made a ticking noise.

I ended IP selling that Jeep, and after I addressed those issues...it was such a quiet and smooth running engine. The clock spring is what caused the horn not to function.