New here& have a mystery to solve.

I friend recommended this site to me, As he said there was a considerable knowledge base here, so I may have a mystery for you to help solve.


I have my Step-dads 1998 4.0 Cherokee sport in the shop, This started out as completely dead, would not start, with a code& symptoms indicating a defective crankshaft position sensor, Which I replaced, I was then able to start the truck, but it still ran extremely rough, at this point I ran out of time to work on it& took it to a shop I trust.
HE has had it& been working on it for a while, he has checked every connection, pulled every wire.
We sent the PCM in for rebuild but it came back as ok.
He was able to find some bad insulation& shiners in the transmission position switch, these he repaired, and the jeep now runs semi rough instead of shaking like a tree in a tornado.
Here's the stumper part when you unplug the transmission sub harness it smooths out. plugged in,it seems to run ok in drive, but if you put it into park or neutral it will set a code in a few minutes. My friend believes has isolated the trouble to the black/white wire from the pcm to the transmission control relay/ transmission control switch. at this point does anyone have have a schematic of the pcm functions, or have any of you encountered this sort of issue before? Are there any special resistance values that should be on the bk/w wire, or is the PCM just looking for a ground?

well this black white wire goes thru the contact side of the relay correct? (not the coil side)

Below is assuming its a standard automotive relay...

If the wire does, you could have burnt up contacts causing goofy readings/bad ground. With it running and if you can safely access this relay, tap the cover of it with a screwdriver handle and see if it changes performance at all. Tapping it will bounce the contacts around and may make it sit better or noticeably change performance in the engine if it sits worse.

Usually with relays electrical arcing burns little pits in the contacts. Over time instead of being 2 flat pancakes they start to look like mountian ranges and sit weird on top of one another causing high resistance/changing resistance.

If jeeps are like GM see if another exact rated relay is nearby that you can "borrow" that wont affect the engine (like a headlight relay) is nearby and swap them. (do it with the engine off/key off...) Then restart the Jeep and see what if anything it does different.

I asked about swapping relays& the mechanic said he tried swapping one just like you say. I think we have tested& looked at all the obvious things, now we are looking for the odd things (the story of my life:jester: )

What is the code?

MAY POP said:

What is the code?

Click to expand...

I'll double check in the morning& get back, but iirc it is related to crankshaft& camshaft position sensors.

The code he was picking up was turbine input sensor.

here are the codes we are getting now
p1391 loss of crankshaft /camshaft position sensor input
p0715 turbine input speed sensor
also tcc.

I have replaced both crankshaft& camshaft position sensors, and although the 1998 isn't supposed to have the turbine input sensor( dealer only item about $150) we have replaced it too.

Never heard of a turbine speed sensor, sounds like the vehicle speed sensor, which the PCM uses to determine engine loads, and when to shift gears.

Is the distributor shaft wobbly?

Check the NSS, neutral safety switch, it may need cleaning internally.

Ecomike said:

Never heard of a turbine speed sensor, sounds like the vehicle speed sensor, which the PCM uses to determine engine loads, and when to shift gears.

Is the distributor shaft wobbly?

Check the NSS, neutral safety switch, it may need cleaning internally.

Click to expand...

The computer compares the readings of the CKPOS & the turbine input sensor to determine torque converter slippage.
I will have to check the distributor shaft for wobble.
the NSS is located in the transmission position switch,a $400 item. there was an O-ring on the transmission that had been leaking& the ATF had degraded the insulation on some of the wire to the TPS. My mechanic repaired those damaged wires& cleared the shorts/grounds resulting from the bare wires. he also tried a new tps from the dealership, but it made no difference in how it ran. and $400 just to say we replaced it was not practical.

Where is this mythical turbine speed sensor located?

Rock auto has the NSS (Older jeeps have one part called an NSS, neutral safety switch, seems the 98 has it split into two parts now, a small single NSS switch, and the larger range finder switch. In 87-90, probably up to 95 or 96, both the range selector and the NSS are one part, called an NSS. I bought 3 of them on close out sale last year for $25 each.

You "Range selector" switch is about $220 at Rock auto:

http://www.rockauto.com/catalog/raframecatalog.php

But the older NSS can be opened up and cleaned and regreased. The contacts get dirty, oxidized. You 98 RSS is probably also repairable, as it looks just like the 87-90 NSS (there is a pictorial thread here on repairing then, which is mostly just a good cleaning), which many of us have cleaned and repaired, by just cleaning the contacts inside it.

The older jeeps have a VSS, vehicle speed sensor that taps off a gear in the transmission or transfer case gears. The ECU can compare that data to the CPS (or CPK, people call the old ones a CPS most of the time, Crankshaft Position sensor), and the NSS gear selection (1-2, 3 or D), or TCU gear selection to get torque converter slipage I think. The VSS also feeds the MPH dash gauge via a mechanical speedometer cable. The 87-90 where mechanical with an electronic sensor under the dash, inline to the cable, that output a VSS pulse to one of the ECU/TCU computers. In 98 I think the TCU and ECU became one computer called a PCM (may in 97?). Somewhere in the 90s the VSS and speedometer cable mechanical speedometer.... were replaced with electronics.

The Chrysler guy Said the Turbine speed sensor became an official item in 1999, but was pretty much a secret in 1998. the sensor is supposed to be on the side of the transmission around where the front pump would be.

Edit to add:
At this point, both the Chrysler Mechanic& my guy suspect an issue with a sensor ground somewhere, however are not sure where to go next. The Chrysler mechanic was confident he could fix it, but it might take 2 hours, or take 10 hours to find& repair the faulty ground. at $100 an hour labor, that is an expensive gamble. for a 1998 with 190K.

Sha-ul said:

The Chrysler guy Said the Turbine speed sensor became an official item in 1999, but was pretty much a secret in 1998. the sensor is supposed to be on the side of the transmission around where the front pump would be.

Edit to add:
At this point, both the Chrysler Mechanic& my guy suspect an issue with a sensor ground somewhere, however are not sure where to go next. The Chrysler mechanic was confident he could fix it, but it might take 2 hours, or take 10 hours to find& repair the faulty ground. at $100 an hour labor, that is an expensive gamble. for a 1998 with 190K.

Click to expand...

That is why I do all my own work. I have seen a few posts the last 12 months where later year jeeps had a transmission ground problem that once located, fixed the problem.

Part of my problem is schedule& free time. and not knowing what to look for on these later models or where to look for them. Plus the added fun of being somebody Else's vehicle, that I have now dropped 500 parts& labor into without much improvement in performance.

Do you know what sensors are on the same circuit& which grounds they share? I am led to believe that often one power circuit would feed up to 6 of these sensors& often one ground will service the same number, where a bad ground on one will cause a back-feed& errors on others on that common power or ground.

I had a few minutes to test on this& based on the suggestion of an old friend, I went back to basics, checking compression& fuel pressures.
Fuel manifold pressure key on, engine off was 42, with the engine running I got right at 50psi.

Compression I tested 1 revolution& after 3 or so to pump up
1 75 100
2 75 105
3 75 115
4 100 125
5 100 125
6 100 125
I didn't run a wet test, as I don't have a pump type oil can to meter out an equal amount for each cylinder.

Based on that data, you need to run a wet compression test before going any further. I just use a quart oil cap or a trigger sprayer. I never measured the oil, just get close to a teaspoon in their and crank away.

105 and 100 is a bit low, may just need oil.

PO 715 is not a listed code in the 99 factory manual.

Nor is this sensor listed in the transmission section of the manual. However, the wiring diagrams do show something called an "input speed sensor."

It connects to terminals 1 and 2 of the transmission control module. Violet/light green is the ground to terminal 1, and red/black is the signal line to terminal 2. The ground for that sensor is independent of the others. The output speed sensor goes to terminals 3 and 4, light green/white to 4 for the signal, dark blue/black to 3 for the ground.

Given the cost of service, it might be worthwhile getting a good ohmmeter and going through the harness one line at a time. Not much to lose except time.

Sha-ul said:

Do you know what sensors are on the same circuit& which grounds they share? I am led to believe that often one power circuit would feed up to 6 of these sensors& often one ground will service the same number, where a bad ground on one will cause a back-feed& errors on others on that common power or ground.

Click to expand...

Correct. But you should make sure the wire terminals connected to these grounds are clean and free from corrosion.

Here's a pic of ground G101, which is for the PCM, TCM , and other sensors, systems. G101 is below the ignition coil. G101 is also that stud forward of the ground marked G101.



Here's a pic of ground G106 which is for the transmission range sensor (NSS), and other systems. G106 is below the harness loom just to the rear of the PCM.

Thank you Sidewinder.

P0715 JEEP - Input Speed Sensor 1 Circuit

Symptoms
-Check Engine Light ON
- Possible shifting problems

Possible causes
- Transmission speed sensor circuit is open or shorted.
- Poor transmission speed sensor circuit connection
- Faulty transmission speed sensor

P0715 JEEP Description
The input speed sensor detects the primary pulley revolution speed and sends a signal to the Transmission Control Module (TCM) and Engine Control Module (ECM).

When is the code detected?
Diagnostic Trouble Code (DTC) P0715 is detected when TCM or ECM does not receive the proper signal from the sensor.

P1391 (M) Intermittent Loss of CMP or CKP.
- Loss of the Cam Position Sensor or Crank Position sensor has occurred. Can be a faulty Sensor, a corroded connector, or damaged wires. All the 5 volt sensors share the same circuit so you may have to expand your diagnostics and testing to other sensors/wire plugs/sensor wire harnesses.