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tps troubles. help please!

njxj4x4

NAXJA Forum User
Location
nj
I have a 97 xj auto 4.0 and my check engin light is on with a tps codes I checked my voltage with the key in the on and at idle I get 4.27 volts when it should be .003 or sokething like that. I pulled the tps off and unpluged it and threw my multimeter on it and I'm still getting 4.something volts witch makes me beleve that the tps could possably still be good. Why would I be getting such a high voltage with the plug unpluged shouldn't it think that its at idle now that (if the censor is bad) the plug is undone? Could I be getting a dead short somewheres? Iv heard that there is another censor the tps works with could that be bad causing extra voltage going where its not to go?
 
Here is how to test the TPS on your 1997.
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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 acordingly 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 deined acceptable range causing the ECU to incorrectly fuel the engine. This is noticable 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.
 
Yeah iv done all that but none of that tells me why my output wire has a load on it when its unpluged from the censor.
 
4.27 Volts at the TPS harness connector is a bit low. FSM says it should be 5 +/- .5 Volts (4.5 - 5.5) from the PCM. Pull the harness connector off the MAP sensor and see what voltage input you get there. It should be the same voltage input from the PCM as the TPS.
 
....none of that tells me why my output wire has a load on it when its unplugged from the censor.

You are not testing the wires, you are testing the sensor.

Voltage on the output wire is normal. Key ON, engine OFF, I get 5.1 volts and 4.3 volts on the body side wire harness plug.
 
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4.27 Volts at the TPS harness connector is a bit low. FSM says it should be 5 +/- .5 Volts (4.5 - 5.5) from the PCM. Pull the harness connector off the MAP sensor and see what voltage input you get there. It should be the same voltage input from the PCM as the TPS.

Yeah the input wire I have 5.something volts that's right but the output wire that I beleve goes to the transmission control unit (as my haynes manual says in the scmiatics in the back) has a load on it even when the plug is not connected I'm not at my truck right now but I beleve it was like 4.2 or close to that. If the plug is not connected to the tps senser the input wire can not put a load on the output. But I'm still getting voltage. Thinking about this now my tcu could have a short in it or be bad ( did recently have about a foot of water inside my xj)
 
You are not testing the wires, you are testing the sensor.

Voltage on the output wire is normal. Key ON, engine OFF, I get 5.1 volts and 4.3 volts on the body side wire harness plug.

Yeah that's what I get if I have the plug pluged into the tps sensor or unpluged. Should have .003 volts or something like that at idle witch I don't have. WOT I should have 4.6 or somewheres around that. I feel like you all helping me are teling me the right stuff but I'm not understanding to well I just don't think there should be a load on the output wire with it unpluged. I am a electrican but for high voltage not lowvolt so this crap is kinda diffrent.
 
Yeah that's what I get if I have the plug pluged into the tps sensor or unpluged. Should have .003 volts or something like that at idle witch I don't have. WOT I should have 4.6 or somewheres around that.

These voltges are the outputs from the TPS to the PCM with the connector attached, and are the product of the 5 volt supply voltage from the PCM passing through a variable resistor in the TPS. These voltages represent the throttle position (as simple as that). As the TB plate linkage is moved from idle to WOT a wiper passes over a resistor, the resultant voltage is sent to the PCM as the TPS Signal. The input tap of the resistor gets the 5 volts, the other resistor tap is the ground.

I feel like you all helping me are teling me the right stuff but I'm not understanding to well I just don't think there should be a load on the output wire with it unpluged. I am a electrican but for high voltage not lowvolt so this crap is kinda diffrent.

With the TPS harness connector detached from the TPS, look at the connector. The pin on your far left is pin 3, which is the 5 volt input from the PCM. The pin in the middle is pin 2, which is the TPS Position Signal (the varied voltage) to the PCM. The pin on your right is pin 1, which is the TPS "Return", or ground within the TPS.

With your DVM read between pins 3 and 1, 5 volts right?

Read between pins 2 and 1, should be zero volts.

The TPS output signal does, in fact, go to the TCM in addition to the PCM. There's a splice in the pin 2 harness that goes to the PCM that takes the signal voltage to the TCM. If you think the TCM is backfeeding the TPS Signal to the PCM, you can detach the connector from the TCM and see what happens.

What code are you getting, you didn't state in your original post?
 
I just unpluged my tcm and I still have 4.5 volts on the output wire so it could be my pcm backfeeding?
 
Now that I plugged it back it my check enegin is off obd II won't read andything and my truck won't start it turns over but won't start. I checked all the fuses disconnected my battory and reconnected it and still nothing I'm so confused now haha
 
If you have TPS codes, it probably is a faulty TPS or TPS wire.

P0122 P0123 Possible causes
- Throttle position sensor harness is open or shorted
- Throttle position sensor circuit poor electrical connection
- Faulty throttle position sensor
 
If you have TPS codes, it probably is a faulty TPS or TPS wire.

P0122 P0123 Possible causes
- Throttle position sensor harness is open or shorted
- Throttle position sensor circuit poor electrical connection
- Faulty throttle position sensor

Ill go to the junk yard and pull one before I get a new one so I don't brake the new one but I still don't unjderstand why there would be voltage on it still. Also I got the truck to turn back on
 
I just checked the voltages at my (disconnected) TPS harness connector.

Here's what I found:

Key Off -

Cavity 2 (signal) to cavity 1 (PCM Ground) - 0.00 volts

Key RUN, engine off -

Cavity 3 (5V source from PCM) to cavity 1 - 5.15 volts

Cavity 2 to cavity 1 - 4.69 volts

Cavity 2 to chassis ground 0.00 volts

Note: I have no CEL or performance problems.

If you are reading similar voltages to the ones I recorded above, your TPS wiring MAY be okay.

Now that the codes are cleared and your truck is running again(?) try driving it for several trips and see if the codes return; however, for the record, you should check your CCD Bus. Refer to the following schematic, and the steps below it.

XJCCDDLC.jpg


Using a digital Voltmeter check for voltages at the DLC.

Battery fully charged.

All modules and sensors connected.

Key RUN, engine off.

Check for approximately 2.50 volts between cavities 3 and 4 or 5 (CCD Bus (+) to DLC Ground)

Check for approximately 2.50 volts between cavities 11 and 4 or 5 (CCD Bus (-) to DLC Ground)

If any voltage is out of range (could be as low as 2.41 volts), disconnect the TCM and retest.

Note all the modules on the CCD Bus. Any one module could cause an out of range voltage on the CCD Bus.

Edit: I have a '99.5 XJ, 4.0, AW4
 
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I forgot to add that the TPS Sensor Return (PCM ground) wire is shared (splice) with the senseor returns (ground) of the Intake Air Sensor and the Engine Coolant Temp Sensor, both of which are supplied with a 5 volt reference from the PCM. The 4.XX volts being read on the TPS signal (cavity 2) wire may be originating from these circuits.
 
Here's some more work for you while you're in the engine bay.

Note the location of G101 is just below the ignition coil.

You may want to check the grounds shown in the pic below for security and evidence of corrosion, and check for wires chaffing on the coil mount bracket.

G101.jpg
 
Every so often I get a engine coolant temp code but it comes and gose last time I looked at the codes it was just showing p0123 when I get home from work today ill try them tests in your last post. My buddy restet my computer last night also thinking that night help but it still shows the p0123 code and now idles funny
 
Here's the basics of P0123:

P0123-THROTTLE POSITION SENSOR VOLTAGE HIGH

Possible Causes

THROTTLE POSITION SENSOR SWEEP
INTERMITTENT CONDITION
THROTTLE POSITION SENSOR SIGNAL CIRCUIT SHORTED TO 5 VOLT SUPPLY CIRCUIT
THROTTLE POSITION SENSOR SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE
THROTTLE POSITION SENSOR INTERNAL FAILURE
SENSOR GROUND CIRCUIT OPEN
THROTTLE POSITION SENSOR SIGNAL CIRCUIT OPEN
PCM

Was your coolant temp code P0118? That's ECT Sensor Voltage too high.

The Clockspring shares the ground (Sensor Return) to the PCM with the TPS, IAT, and ECT sensors through splice S111. There's an odd chance that there is a voltage leak in the clockspring to the sensor return circuit. It may not be the full battery bus voltage (12 volts) but enough to screw things up in the TPS, ECT, and IAT. It may only occur when the streeing wheel is turned.

12 volts is made available at the clockspring from the horn relay. The horn relay is waiting for a ground to activate the relay, which powers the horn(s). You can try removing the horn relay and see if your problem persists. It's located in the Junction Block, in the passenger footwell. You will have to remove the cover off the JB to access the relay. I don't have a clear pic of the JB but the pic below catches the very edge of the relay. It's the second relay up from the bottom (the edge of it can be seen under the wording on the pic pointing out the radiator fan coil fuse).

XJ97_99JUNCBOX.jpg


TPS, IAT, and ECT will affect engine performance, they all work together to determine fuel injector pulse width.
 
Test the TPS according to the instructions provided. You are looking for the results noted, and nothing else.

Randomly probing things and then attempting to interpret the data without knowing what the data should be, is non-productive.

As I noted, on the body side of the TPS wire plug, 1997-2001, Key ON, engine OFF, TPS unplugged, you have a ground wire, a 5 volts supply wire, and approximately 4.3 volts on the remaining wire.
 
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Thank you everyone for the help got it all fixed turns out the tps was bad and my tcu tcm whatever one you wanna call it was shorted out sending a 5v back up the output wire. Just did this all today and still gotta drive ir around alittle to make sure what I did did fix it but till then thank you everyone for the help
 
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