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  #1  
Old February 2nd, 2017, 20:43
Heavyopp Heavyopp is offline
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Throttle position sensor - Voltage on output wire

Need some help -- been reading for days looking for answers

2000 Cherokee sport -- 225,000 miles bought it 2 months ago for $200 -- barely any rust -- zero rot anywhere

Here's what I know -- Right now throwing codes P0123, P0122, P1694 -- barely idles, runs rough off idle -- California emissions -- glowing red exhaust pipe for 6 inches after rear pre cat only also red at bottom of pre cat housing but only rear pre cat

In diagnosing a bad TPS i get some weird voltage readings -- 5.2 volts on voltage input pin -- Ground pin seems good also but I get 4.32 volts at the TPS output pin -- this is with the TPS UNPLUGGED -- all these readings are at the wire connector -- 4.32 volts coming from the PCM for the TPS signal pin -- shouldn't it be 0 volts

In searching and reading here I've tried a few things on the few threads I can find with similar problems -- I've pulled the horn relay to eliminate a clock spring issue -- I've also gone thru and cleaned up all the grounds I can find

I also checked the PCM -- Unplugged wire harness "A" and tested the pins on the PCM

pin 17 is 5 volt output to sensors -- I get 7 volts at pin 17 with harness "A" unplugged

Pin 23 is input from TPS -- I get 6 volts at this pin when harness is unplugged -- Shouldn't it be 0 and waiting for input from TPS?

Once I plug in harness "A" and test at TPS connector my voltages drop to 5.2 for the 5 volt input and 4.32 for the middle wire -- the one for TPS output

I'm lost -- Do I have a faulty PCM? -- By unplugging the wiring harness from PCM and still getting voltage at pin 23 I have eliminated a problem in the wiring harness - correct?

Thoughts? Should I be looking for a PCM, it's a 635 AG?

Jer
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  #2  
Old February 2nd, 2017, 20:49
Heavyopp Heavyopp is offline
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Re: Throttle position sensor - Voltage on output wire

Forgot to mention that the XJ came to me without the exhaust pre cat "Y"pipe -- I bough a new one -- Walker -- and I re-welded all the joints because it was so poorly done -- I also had replaced all 4 O2 sensors with NTK sensors -- and I did replace the blown O2 fuse

I also replaced all 6 fuel injectors with the upgrade mustang injectors -- I forget the part number but I can get them if important

also 6 champion plugs -- I have the NGK's but waiting to install them till I figure out this TPS issue
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  #3  
Old February 3rd, 2017, 07:38
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90xj06 90xj06 is offline
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Re: Throttle position sensor - Voltage on output wire

so P1694 could be melted wires on the crank sensor. but seeing its starting im not sure if that the cause. does it drive ok?

also the red exhaust is its either running rich or the cat is clogged.
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  #4  
Old February 3rd, 2017, 09:09
Heavyopp Heavyopp is offline
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Re: Throttle position sensor - Voltage on output wire

Barely runs at idle -- can move it around the yard but haven't tried to drive it on the road --

Any suggestions on why there would be voltage on the TPS "input" pin on the PCM? That pin should be waiting for voltage from the TPS not supplying voltage to the TPS.
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  #5  
Old February 3rd, 2017, 18:18
westvirginia24976 westvirginia24976 is offline
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Re: Throttle position sensor - Voltage on output wire

I can't take credit for this, but I copied and pasted this to my son and it was easier for me to find in my sent emails than to search here. Cured his P0123. Jeep runs great now.






A Clock Spring TPS fault usually sets a P0123 trouble code. Your codes suggest a wiring issue which could be on any one of the 5 volt sensors. You probably need to expand you inspection and testing of the wire harness.


P0122 JEEP - Throttle Position Sensor/Accelerator Position Pedal Circuit Low Input

Possible causes
- Throttle position sensor harness is open or shorted
- Throttle position sensor circuit poor electrical connection
- Faulty throttle position sensor
- Faulty Powertrian Control Module (PCM)

P1694 Fault In Companion Module. No CCD/J1850 bus messages received from the power train control module-Aisin transmission.

Possible Causes:
CCD Bus (-) circuit open between PCM and TCM.
CCD Bus (+) circuit open between PCM and TCM.
Transmission CCD bus wiring damaged.
Faulty TCM.


COMPLAINT: TPS CODE P0123 WILL NOT CLEAR

A late model Jeep with a 2.5 or 4.0 liter engine and the AW4 transmission comes in with the “MIL” Check Engine Light illuminated and a complaint of late shifts. A scan reveals a code P0123, “TPS Voltage High”, is stored. The scan tools data list indicates that the TPS signal wire voltage is at 5.0 volts at closed throttle, and then ranges up to 11.5 volts. A back probe of the TPS signal wire (usually is an Orange/Dk Blue wire), shows 5.7 volts at closed throttle, with a similar rise in voltage as the throttle is opened. A check of the TPS 5 volt supply and ground circuit prove that both of these circuits are good.

A check of the TPS signal wire with the TPS disconnected shows the same 5.7 volts. Inspection of the wiring between the TPS and the PCM and TCM shows no faults. A replacement TPS does not cure the problem, neither does replacement of the PCM or TCM.

CAUSE:
The Switch Sense circuit in the Clock spring in the steering wheel hub has shorted to battery voltage from the horn button circuit. When the Switch Sense Circuit shorts to the 12 volt HORN circuit the TPS signal voltage is driven high and remains there as shown. This is because the 5 volt reference voltage used by the Cruise Control “Switch Sense” circuit and the TPS are shared inside the PCM.

TESTING:
Unplugging a faulty Clock Spring should return TPS voltages to the normal readings.

CORRECTION:
Replace the Clock spring assembly. Once the Clock spring has been replaced be sure to check the sensor 5volt reference voltage at the PCM to insure that circuit has not been damaged by the short to power. Also check the TPS signal range to insure the TPS has not been damaged.
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  #6  
Old February 3rd, 2017, 20:12
Heavyopp Heavyopp is offline
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Re: Throttle position sensor - Voltage on output wire

Quote:
Originally Posted by westvirginia24976 View Post
I can't take credit for this, but I copied and pasted this to my son and it was easier for me to find in my sent emails than to search here. Cured his P0123. Jeep runs great now.
I just read about this on the forum yesterday -- Short in the clock spring

One of the tests I read about was to pull the horn relay -- that should eliminate the 12 volt power supply in the steering wheel

I did pull the relay for the horn -- No Change -- I'll try and locate the clock spring harness at the bottom of the steering column and unplug -- See if that changes anything

Also I do not have cruise control as far as I know -- It certainly isn't on the steering wheel -- Not sure if all XJ had the wiring for the cruise control circuit up in the steering column no matter if the jeep had cruise or not

I wonder if there are 2 different clock spring part numbers -- one with one without cruise

Thanks for the reply, guess it can't hurt to chase down that connector and unplug it
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  #7  
Old February 3rd, 2017, 20:19
Heavyopp Heavyopp is offline
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Re: Throttle position sensor - Voltage on output wire

just checked rock auto -- there certainly are 2 different mopar part numbers for clock springs with and without cruise/speed control
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  #8  
Old February 3rd, 2017, 21:47
westvirginia24976 westvirginia24976 is offline
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Re: Throttle position sensor - Voltage on output wire

Horn relay won't do it. Must unplug the clockspring. My son tried that too.
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  #9  
Old February 3rd, 2017, 22:28
Heavyopp Heavyopp is offline
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Re: Throttle position sensor - Voltage on output wire

Sounds promising -- I'll certainly try that tomorrow
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  #10  
Old February 3rd, 2017, 22:53
Heavyopp Heavyopp is offline
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Re: Throttle position sensor - Voltage on output wire

So been looking around -- can't find an answer

Is it possible to disconnect the clock spring at the base of the steering column or is the only plug for the clock spring behind the assembly itself?
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  #11  
Old February 4th, 2017, 13:01
JeepNoob JeepNoob is offline
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Re: Throttle position sensor - Voltage on output wire

On my '96, the TPS signal wire always has a little bit of voltage on it, even with it unplugged, but nothing like 4 volts, more like 1/2 a volt or so. No idea why it's like that, but it doesn't throw any codes, so I suspect it's an OEM design feature of some sort. I wouldn't rule out an internally shorted PCM, but I'd try to rule out all other possibilities first.

Last edited by JeepNoob; February 4th, 2017 at 13:04.
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  #12  
Old February 4th, 2017, 17:43
Heavyopp Heavyopp is offline
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Re: Throttle position sensor - Voltage on output wire

Can rule out the clock spring -- I took the 3 screws out to gain access to the clock spring and unplugged it -- With no cruise control I only have 3 wires in the harness

I also did some testing and it's really looking like a bad PCM -- doesn't seem to be a shorted wire -- no chaffing in any of the wiring harnesses

I also went thru all the grounds I could find -- took apart, cleaned with wire wheel, and reassembled with some copper never seize made for electrical connections -- While I was at it I made a jumper wire for the ground at the dipstick bolt to tie it into the nearest ground on the engine block

I guess I'm going to have to find a PCM -- its a 635ag if anyone has a source or has one laying around
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  #13  
Old February 5th, 2017, 00:25
Waynerd Waynerd is offline
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Re: Throttle position sensor - Voltage on output wire

With my 98 I pulled the 2 horn fuses and the air bag fuse. I confirmed by checking my other 98 that there is voltage to the signal wire at the plug when it's disconnected from the TPS. I had a thread going in the past and no one could answer why. Also Google false TPS codes. There are other causes apparently.
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  #14  
Old February 5th, 2017, 01:04
Heavyopp Heavyopp is offline
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Re: Throttle position sensor - Voltage on output wire

Quote:
Originally Posted by Waynerd View Post
With my 98 I pulled the 2 horn fuses and the air bag fuse. I confirmed by checking my other 98 that there is voltage to the signal wire at the plug when it's disconnected from the TPS. I had a thread going in the past and no one could answer why. Also Google false TPS codes. There are other causes apparently.
So what ended up being the cause for You?

Did it turn out to be A bad pcm?

If I could find another 635ag PCM locally I'd love to just try a swap before buying a pcm on a hunch with no real way to confirm its bad

I hate being a parts changer and needlessly buying and swapping parts that aren't bad
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  #15  
Old February 5th, 2017, 09:30
Heavyopp Heavyopp is offline
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Re: Throttle position sensor - Voltage on output wire

Just found a 635ag PCM on eBay -- seller accepted my offer $55 -- 90 day warranty
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