Emusoda

Alright so I'm trying to figure out if im being bull****ted or not. I've been having problems with my tps and brought it to a shop to get it looked at. They hooked it up to a scanner and got a couple codes (P0122, P0123). I've got the usual rough idle and almost stalling symptoms. Now the shop I brought it to said that he couldn't figure out why it was acting the way it was and throwing the codes so he brought in one of his friends who specializes in Chrysler vehicles. He hooked up this DRB3 scanner and did some stuff. Now I'm being told i need a new TCM for my transmission. Now I know that the TPS the ECU and the TCM are all connected but why would it be throwing codes for the TPS if the problem is with the TCM? I also got the common P0700 code but I think that has to do with my NSS because I go mudding and it probably got full of water. What do you guys think of this?

Here is some more info:
Jeep shifts fine
Trans fluid level is normal
243xxx miles
Auto AW4 trans
4.0 engine

Bob98Classic

Since you have went mudding, check under the distributor cap for any moisture or mud. My cam sensor there was bad as well as my CPS.
You can check the voltage of the cam sensor, and CPS, to see if they
have the correct voltage....

Emusoda

Is the CPS tied into the TPS and TCM?

CCKen

No.

There are threads that explain how to test your TPS, just search for them/it using Google. Just put "Cherokeeforum" before your search terms and it should bring you to the procedures.

Emusoda

The guy tested it with his scanner. He told me from the ECU it was showing about 90% of standard voltage but from the TCM it was showing 150% which he said was impossible and that is why he thinks the TCM is bad

CCKen

Before going to the expense of replacing the TCM perhaps you shpould address the TPS first.

tjwalker

I agree with Ken. With the codes you are seeing, verifying/testing the throttle position sensor should come before condemning the TCM. Here's more on this very important engine management sensor. If you decide to install a new TPS, do yourself a favor and buy a genuine MOPAR unit from your Jeep dealer. There are many crap engine mgmt. sensors on the market. Good luck!
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The throttle position sensor is connected to the throttle shaft on the throttle body. It sends throttle valve angle information to the PCM. The PCM uses this information to determine how much fuel the engine needs. The TPS is really just a simple potentiometer with one end connected to 5 volts from the PCM and the other to ground. A third wire is connected to the PCM. As you move the accelerator pedal with your foot, the output of the TPS changes. At a closed throttle position, the output of the TPS is low, about a half a volt. As the throttle valve opens, the output increases so that, at wide open throttle, the output voltage should be above 3.9 volts. Testing can be performed with an electrical meter. Analog meter is best. You are looking for a smooth sweep of voltage throughout the entire throttle band. While slowly opening and closing the throttle, take note to the movement of the voltmeter needle. There should be a direct relationship between the needle motion to the motion of the throttle. If at anytime the needle moves abruptly or inconsistently with the movement of the throttle, the TPS is bad

You should have 5 volts going into the TPS. At idle, TPS output voltage must be greater than 200 millivolts. At wide open throttle (WOT), TPS output voltage must be less than 4.8 volts.. The best is to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. One of the other wires should show .26V (or so). The other wire will be the ground and should show no voltage. Move the throttle and look for smooth meter response up to the 4.49 at WOT.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.

The TPS is sensitive to heat, moisture and vibration leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following: -

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics! It should be verified early in the troubleshooting process, when a transmission issue is suspected!

• Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".
• High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.
• Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.
• Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted accordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.
• Engine Misfire: A fault TPS can report values outside the denied acceptable range causing the ECU to incorrectly fuel the engine. This is noticeable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessing misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.

Emusoda

I'll give this a shot when I get the chance. I already knew that the tps was connected to the tcm. It sucks that this guy charged me $70 for hooking his computer up and trying to tell me that it's the tcm and not the tps

EMAXX620

As mentioned, go get a MOPAR tps. I got sick of BWD and autozone sensors. Yeah, it's great they have a lifetime warranty and all... but my last warranty swap on a autozone tps died the SAME day... Put it in, cleared the code, drove home... same issues. Gave it 2 days and had the same issues, went to the dealership and got a MOPAR sensor and no problems since.

A bad CPS can cause a whole lotta different issues, usually ending in it not starting at all. It will crank and crank, maybe occasionally starting, but will misfire like crazy then die. Mine started to bog down at lights and stall (thought it was a crappy TPS again)

Emusoda

Ok so I tested the tps and I think it's ok but I'm unsure. Here is a video of me moving the throttle while having my multimeter hooked into the middle wire.

http://s186.photobucket.com/user/emu...61278.mp4.html

rompnXJ

that diagnosis doesnt really make sense.
lets assume there was a short to power to the TPS circuit inside the TCM. this means there will be an excessive voltage reading along the entire TPS circuit, and if he were to plug in a scanner and check the signal, the voltage would be the same along the entire circuit; I.E., all along the wire, at the TPS input pin on the ECM connector, at the TPS signal output pin on the TPS connector, and at the TPS input pin on the TCM connector. he would not be able to see different voltages in different places of the circuit if he just plugs a scanner in.

test his theory. if the jeep is misfiring/stumbling at idle, unplug the TCM and see if the engine smooths out. if it does, go get another one from a junkyard for 20 bucks.

but seeing as how you have codes p0122 & p0123, TPS signal circuit low, AND TPS signal circuit high, you're probably going to find that your TPS is bad.

Emusoda

Update: So I got a new tps and tps pigtail and wires. I was tracing the wires back up the loom to see if there were any breakages and noticed this


Is this how the stock wiring is supposed to be? It doesn't really make sense to me that there would be shrink wrap on wiring harness unless they spliced two wires together from the factory

rompnXJ

I'm creating a standalone OBD1 harness by trimming down a factory harness, the harness had shrinkwrapped splices EVERYWHERE.

The signal wire leaves the TPS, and splits into 2 in the engine bay, 1 goes to the ECM and 1 goes to the TCM.

ECM needs the signal for fuel & TCM needs the signal for shifting

Emusoda

Ok so I got a new pigtail but I forget how the wiring is supposed to be. The wires I have are orange, orange with blue stripe and brown with yellow stripe