Crankshaft / Camshaft Position Sensor Voltage

[Nevadaboy]

2004 Wrangler Sport 4.0 M/T
Hello, Thought maybe with all the info in this forum i could solve my issue buy to no avail so here i am! my dad starting noticing the jeep losing some power & hesitating on his 30mi one way to work, its had the TPS P0122 code for awhile i would just clear it & it would go away, it would run fine around town until last week it shut down on the highway & wouldnt start so had to get it towed. the next morning fired right up & drove fine around town but dad decided it was the fuel pump so before i could test the fuel pressure he already dropped the tank & got a new pump, put the pump in fires right up, its holding about 50psi, so all was good until it wasnt same senario shut down on the highway except this time i got 3 codes P0122, P0340 & P1391 so i cleared them drove around town now only the P0122 has come back, i dont have a scope just my multimeter so i just started checking the wiring, so with the key on i pulled the connector off the cam sensor & im reading 5v on both the reference & signal wire so i left the connector off & checked the crank & throttle position sensor wiring connectors same thing 5 volts to both wires i didnt think the signal wires should have any voltage unless they were hooked up to the sensors an sending a signal back to the PCM ! i finally found a schematic & pinout & it seems i forgot to check the map sensor since it uses the same 5v reference circuit but i assume it will be the same i just want to know if that signal wire should have voltage when not connected to the sensors so thats where im at i dont want to start throwing expensive mopar sensors at it unlssvim pretty sure of the problem, somebody even menioned plugged cats but i would think it would run like crap all the time if that was the case, anyways sorry so long but im just trying to describe this the best i know any help would be appreciated trust me lol ive read some of the nightmares ppl have & i can sympathize with thm! Thanks

 

[Jezza]

Most PCM sensor input channels have a pull up resistor inside the PCM. When disconnected that resistor will usually pull the voltage on that pin up to 5v. FWIW it is best practice to only test voltage on PCM outputs and unplugging the PCM and performing continuity tests on the harness only when testing input circuits.

 

[ItchyDong]

That’s called bias voltage and is an excellent way to verify signal continuity to the PCM, but a bad way to check for sensor operation. One way to see the operation of the sensor without a scope is to back probe the sensor or the pcm signal wire and to slowly rotate the engine in the direction of rotation by hand with a socket on the crank. You should see your multimeter jump from 5 to near zero volts. You can also bump the starter to get the tone wheel in various positions to check for 5 and zero.

Understand that what that doesn’t show you is a clean square wave as it would on a scope.

 

[ItchyDong]

The P0122 code could be tested with key on engine off, back probing signal wire and monitoring the voltage while sweeping the throttle. Or, unplugged, key off, and running continuity through the sensor while doing the same throttle sweep. Oooor, graphing live data for tps and sweeping throttle.

 

[Nevadaboy]

The P0122 code could be tested with key on engine off, back probing signal wire and monitoring the voltage while sweeping the throttle. Or, unplugged, key off, and running continuity through the sensor while doing the same throttle sweep. Oooor, graphing live data for tps and sweeping throttle.

Thanks for the reply, welp looks like i have my marching orders this morning, so would it be safe to say that the tps isnt the culprit for the stalling or the no start after it stalls? im assuming that the tps doesnt have the authority to create a no start situation or does it? ill start with that work my way around & im in podunk Nevada where the nearest auto parts store is 75mi so parts are always 2 days out even with overnight, gotta love it!

 

[Nevadaboy]

Most PCM sensor input channels have a pull up resistor inside the PCM. When disconnected that resistor will usually pull the voltage on that pin up to 5v. FWIW it is best practice to only test voltage on PCM outputs and unplugging the PCM and performing continuity tests on the harness only when testing input circuits.

Ok that makes a little more sense to me, some of it is still above my pay grade but hopefully we can get this figured out them Salmon over there in the Rouge River Bay in Oregon aint going to wait for me much longer! Thanks for the reply

 

[ItchyDong]

Thanks for the reply, welp looks like i have my marching orders this morning, so would it be safe to say that the tps isnt the culprit for the stalling or the no start after it stalls? im assuming that the tps doesnt have the authority to create a no start situation or does it? ill start with that work my way around & im in podunk Nevada where the nearest auto parts store is 75mi so parts are always 2 days out even with overnight, gotta love it!

The tps can absolutely cause a no start. If it’s a no crank, that’s a different story. I’d try to do my troubleshooting when it’s acting up. Backprobe the tps signal and at idle it should be reading around 1volt. Pin fitment is also a concern being that it’s intermittent, but it could also be heat related.

Really, live data would be your friend here because it’s non intrusive and you could drive it while monitoring it. If you do end up going to a parts store, a cheap scan tool would be a good thing to pick up. You could view freeze frame data for what tripped the code.

 

[hear]

Thanks for the reply, welp looks like i have my marching orders this morning, so would it be safe to say that the tps isnt the culprit for the stalling or the no start after it stalls? im assuming that the tps doesnt have the authority to create a no start situation or does it? ill start with that work my way around & im in podunk Nevada where the nearest auto parts store is 75mi so parts are always 2 days out even with overnight, gotta love it!

The TPS does sort of have the authority to tell the ASD to shut things down. That 5V reference is supplied to all the important sensors, so if there is any trouble in that wiring it could present as a cam, crank, map, tps, etc. The sensors all use the same ground as well (I haven't actually traced the wiring, but all the sensors use circuit K167 for ground and at least on my 97 there is only one ground pin at the PCM [meaning each sensor doesn't have it's own ground at the computer]), so yeah, any of those sensors can ruin your day.

What I have found more often than not is that the insulation around the sensor plugs shrinks over time & exposes the wiring. Then they get twisted, and you can end up with an intermittent short that results in a crank/no-start. But it could also be within the harness, particularly right behind the valve cover where it can wear through the loom & insulation.

This picture didn’t end up focusing very well but you can see what I’m talking about. The Jeep this came off ran fine for a long time and then one day it just wouldn't start and eventually traced it to this. Apparently it was on the razor's edge, and then it must've got bumped in just the right way. It can be a fine line between running great and not starting.