BlackXJay

Okay so while driving I noticed my idle jumping a little. At a traffic light it died. I pushed it into a safe spot. So I checked and found 2 codes. I had a p0122 and p0123 . Tps. The car will not start. Can a bad tps cause a no start? I checked the wiring all seems fine .


99 4.0

Thanks

BlueRidgeMark

Yes, a bad TPS can certainly cause a no-start.

It can also cause idle jumping a little. It can also cause dying at traffic lights.

With two codes pointing to the TPS, I'd say you just might have a bad TPS.

Use OEM only on those. Our 4.0s do not like aftermarket. Not even good stuff like Bosch. You may find it at NAPA (NTK brand) cheaper than the dealer (NGK brand). They are the same.

BlackXJay

Okay tmw I will try a new tps from a dealership and see what the results are. Thanks

BlackXJay

Well i went to the dealership and changed the tps. Same problem of just cranking but no start. Still have the same code. Without a quick fix I checked for spark and have none. What's my next step??? I hear a lot about the crank position sensor going bad but I don't want to keep throwing money at the problem. Thanks

BlackXJay

I have also checked all my grounds. New battery. Checked starter connection.

Programbo

You can try the CPS. Maybe even look at the MAP sensor. Hopefully it's something simple. I had 2 bizarre sensor problems on my '94 XJ and the one took me 2 years to figure out and fix

BlackXJay

Yes It is frustrating. Would a bad cps cause the car to die while driving.? What is a good procedure in testing the cps?

jordan96xj

Yes, a bad CPS can cause a car to die while driving. It will also cause no starts. If it has partially failed (sending improper readings to the computer) it can also cause bad running (instead of total failure).

There are quite a few posts here and other places on how to test. The following will at least test the electrical connections through the sensor. If they check out good, unfortunately, they do not rule out a CPS that is electrically connected properly, but sending poor readings to the computer (for example because the magnet in the sensor is going bad, or because the sensor has gotten too far from the tone ring/fly wheel, or because the fly wheel is damaged).

https://www.cherokeeforum.com/f51/testing-cps-5563/

Signal problems from the sensor are typically diagnosed by viewing the signal on a scope of some type (digital storage oscilloscope, automotive diagnostic scope like snap-on, etc) and comparing the sensor's signal to a known good pattern, or simply knowing what the pattern should look like due to experience with the particular vehicle.

This article gets into the signals involved/wave forms of the sensor (uses a 1996 Jeep Grand Cherokee 4.0 I6 in the article):

http://www.underhoodservice.com/the-...o-a-breakdown/

Jeepin'_Aint_EZ

If you have no spark then start at the spark plug and work your way up stream. A bad coil could cause no spark and is much much easier to change than a cps

BlackXJay

Okay thanks guys. I have no access to the truck right now bc I am out of the state for a couple of days. But I am confused about the fact it is throwing a tps code. I did a quick inspection of the wiring and all looked good. Will a bad tps cause no spark? Bc as stated above I have no spark. I just want to rule out the tps or dig deeper and check the wiring.

Also should mention I have LeBaron hood vents and read up on a lot of people having trouble with tps sensors bc of water and freezing. I have changed the sensor with a mopar with no help.....

Programbo

Don't let the codes you are getting fool you. For years I would get TPS codes. My XJ would run fine up the highway but as soon as I got off and stopped at a red light or slowed the check engine light would come on and it would run terribly. The code always said TPS. This went on for years. I tried everything. Finally one day my Jeep wouldn't start. Just cranked. I was getting a MAP sensor code.

After a day of scratching my head I had the Eureka! moment. Both the TPS and the MAP sensor had a purple and white wire coming off them which combined to become a single wire inside the wiring harness and continuing on to the computer. Somehow where they joined had broken or lacked sufficient strands to carry a full signal and the purple and white wires were then only connecting the 2 sensors together. So once I stopped or suddenly slowed the MAP sensor would try to send a signal to the computer. The signal would go to the TPS instead which read this as incoming voltage and would start to adjust the engine to compensate and I'd get the rough idle and stalling and TPS code. I cut and re-soldered this wire junction and the problem went away forever! I had a similar problem getting a rough idle and O2 sensor code.

​​​​I'm not saying this is your problem but it sounds similar and it shows sometimes codes aren't what they seem and you need to think "outside the box".

BlackXJay

Thanks program... well after a night of research I found that various sensors use a 5v reference and can cause false codes.....such as p0123..... so if matters weren't bad enough I'm on a wild goose chase. But when I get back to the car I'm going to clean all connections and start checking the sensors with a multimeter and work on it from there.

Waynerd

Myself I had continuos TPS codes as well. I was experiencing symptoms like a bad TPS also. The only way I was able to resolve it was removing horn and airbag fuses. There's a known issue of the clockspring causing problems with the sensor ground shorting. But mine was beyond that somehow. I have since given up on that issue until I can afford a clockspring. I did read that it most often shows as a TPS code.

My issue wouldn't cause no spark but perhaps this condition in other areas of the wiring would also cause a TPS code. Seems as though maybe TPS is most sensitive and there are more often false codes for the TPS than any other sensor.

BlackXJay

Well the prize goes to jeepin. Turned out to be the ignition coil. I had my money on the cps. Still so weird it was throwing a tps code.....I cleared the code and it hasn't come back. Thanks everyone!

Jeepin'_Aint_EZ

Well, I award myself this time