I have a 2002 jeep grand cherokee v8 4.7l that has a indicator code reading p0121. i changed the tps and the check engine light is still on and it still reads the same indicator code. any ideas what might still be the problem?

Hi there:

DTC P0121 - Throttle Position Sensor/Switch A Circuit Range/Performance Problem


The Throttle position sensor is a potentiometer that measures the amount of throttle opening. As the throttle is opened, the reading (measured in volts) goes up. The powertrain control module (PCM) supplies a 5 Volt reference signal to the throttle position sensor (TPS) and usually a ground also. A general measurement is: at idle = .5 Volts; full throttle = 4.5 Volts. If the PCM detects that the throttle angle is greater or less than it should be for a specific RPM, it will set this code.





Symptoms of a P0121 trouble code could include:
* Malfunction Indicator Lamp (MIL) illumination (Check Engine Light or Service Engine Soon light)
* Intermittent stumble on acceleration or deceleration
* Blows black smoke on acceleration
* No start




A code P0121 may mean that one or more of the following has happened:
* TPS has intermittent open or short internally
* Harness is rubbing and causing an open or short in the wiring
* Bad connection at the TPS
* Bad PCM (less likely)
* Water or corrosion in connector or sensor





Possible Solutions:
1. If you have access to a scan tool, see what the idle and WOT (wide open throttle) readings are for the TPS. Check if they're close to the specifications mentioned above. If not, then replace the TPS and re-check.
2. Check for an intermittent open or short in the TPS signal. To do that, you can't use a scan tool. You'll need an oscilliscope. The reason is because scan tools take samplings of many different readings over just one or two data lines and can miss an intermittent drop out. Hook up your oscilliscope and watch the signal. It should sweep up and down smoothly with no drop outs or spikes.
3. If no problems were noticed, perform a wiggle test. Do this by wiggling the connector and harness while watching the pattern. Does it drop out? If so, replace TPS and re-check.
4. If you have no TPS signal, check for 5 Volt reference at the connector. If it's present, check the ground circuit for open or shorts.
5. Make sure the signal circuit isn't 12V. It should never have battery voltage. If it does, trace circuit for short to voltage and repair.
6. Look for any water in the connector and replace TPS as necessary.


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You need to read the computor, I believe if you turn the ignition three times without starting it, and the engine lite will blink, that is how you read the codes, long blinks are ten, two long blinks is 20, and the faster blinks are one, get back to me what the codes are and i'll help you.

DTC P0121 - Throttle Position Sensor/Switch A Circuit Range/Performance Problem
The Throttle position sensor is a potentiometer that measures the amount of throttle opening. As the throttle is opened, the reading (measured in volts) goes up. The powertrain control module (PCM) supplies a 5 Volt reference signal to the throttle position sensor (TPS) and usually a ground also. A general measurement is: at idle = .5 Volts; full throttle = 4.5 Volts. If the PCM detects that the throttle angle is greater or less than it should be for a specific RPM, it will set this code.

Symptoms of a P0121 trouble code could include:
Malfunction Indicator Lamp (MIL) illumination (Check Engine Light or Service Engine Soon light)
Intermittent stumble on acceleration or deceleration
Blows black smoke on acceleration
No start

A code P0121 may mean that one or more of the following has happened:
TPS has intermittent open or short internally
Harness is rubbing and causing an open or short in the wiring
Bad connection at the TPS
Bad PCM (less likely)
Water or corrosion in connector or sensor

Possible Solutions:
1. If you have access to a scan tool, see what the idle and WOT (wide open throttle) readings are for the TPS. Check if they're close to the specifications mentioned above. If not, then replace the TPS and re-check.

2. Check for an intermittent open or short in the TPS signal. To do that, you can't use a scan tool. You'll need an oscilliscope. The reason is because scan tools take samplings of many different readings over just one or two data lines and can miss an intermittent drop out. Hook up your oscilliscope and watch the signal. It should sweep up and down smoothly with no drop outs or spikes.

3. If no problems were noticed, perform a wiggle test. Do this by wiggling the connector and harness while watching the pattern. Does it drop out? If so, replace TPS and re-check.

4. If you have no TPS signal, check for 5 Volt reference at the connector. If it's present, check the ground circuit for open or shorts.

5. Make sure the signal circuit isn't 12V. It should never have battery voltage. If it does, trace circuit for short to voltage and repair.

6. Look for any water in the connector and replace TPS as necessary.


Hope ths helps; keep us updated.

Depending on the system, P0121 is Throttle/pedal position sensor/switch A circuit range/ performance problem.

Did the TPS have slotted mounting holes? If so it may need to be adjusted.

P0121 - Throttle Position Sensor/Switch A Circuit Range/Performance Problem

The Throttle position sensor is a potentiometer that measures the amount of throttle opening. As the throttle is opened, the reading (measured in volts) goes up. The powertrain control module (PCM) supplies a 5 Volt reference signal to the throttle position sensor (TPS) and usually a ground also. A general measurement is: at idle = .5 Volts; full throttle = 4.5 Volts. If the PCM detects that the throttle angle is greater or less than it should be for a specific RPM, it will set this code.

Potential Symptoms: Symptoms of a P0121 trouble code could include:
Malfunction Indicator Lamp (MIL) illumination (Check Engine Light or Service Engine Soon light)
Intermittent stumble on acceleration or deceleration
Blows black smoke on acceleration
No start

Causes: A code P0121 may mean that one or more of the following has happened:
TPS has intermittent open or short internally
Harness is rubbing and causing an open or short in the wiring
Bad connection at the TPS
Bad PCM (less likely)
Water or corrosion in connector or sensor

Possible Solutions:
1. If you have access to a scan tool, see what the idle and WOT (wide open throttle) readings are for the TPS. Check if they're close to the specifications mentioned above. If not, then replace the TPS and re-check.
2. Check for an intermittent open or short in the TPS signal. To do that, you can't use a scan tool. You'll need an oscilliscope. The reason is because scan tools take samplings of many different readings over just one or two data lines and can miss an intermittent drop out. Hook up your oscilliscope and watch the signal. It should sweep up and down smoothly with no drop outs or spikes.
3. If no problems were noticed, perform a wiggle test. Do this by wiggling the connector and harness while watching the pattern. Does it drop out? If so, replace TPS and re-check.
4. If you have no TPS signal, check for 5 Volt reference at the connector. If it's present, check the ground circuit for open or shorts.
5. Make sure the signal circuit isn't 12V. It should never have battery voltage. If it does, trace circuit for short to voltage and repair.
6. Look for any water in the connector and replace TPS as necessary.

Other TPS sensor and circuit related DTCs: P0120, P0122, P0123, P0124

Yes.
The TPS is thottle position sensor. This is a key data source for the Engine Control Unit adjusting the fuel injection and the ignition.
Failed sensors will put the system into a "limp home" mode. It runs, but all of the fine control used to make maximum power and maximum gas milage is turned off. You should get this fixed.

TPS stands for throttle position sensor, this part is located on the side of the throttle body

What does that mean? The Throttle position sensor is a potentiometer that measures the amount of throttle opening. As the throttle is opened, the reading (measured in volts) goes up. The powertrain control module (PCM) supplies a 5 Volt reference signal to the throttle position sensor (TPS) and usually a ground also. A general measurement is: at idle = .5 Volts; full throttle = 4.5 Volts. If the PCM detects that the throttle angle is greater or less than it should be for a specific RPM, it will set this code.
FB.init("dd7d9e9681341cde77587bc6a2029f6f"); OBD-Codes.com on Facebook Potential Symptoms Symptoms of a P0121 trouble code could include:

• Malfunction Indicator Lamp (MIL) illumination (Check Engine Light or Service Engine Soon light)
• Intermittent stumble on acceleration or deceleration
• Blows black smoke on acceleration
• No start

Causes A code P0121 may mean that one or more of the following has happened:

• TPS has intermittent open or short internally
• Harness is rubbing and causing an open or short in the wiring
• Bad connection at the TPS
• Bad PCM (less likely)
• Water or corrosion in connector or sensor

Possible Solutions 1. If you have access to a scan tool, see what the idle and WOT (wide open throttle) readings are for the TPS. Check if they're close to the specifications mentioned above. If not, then replace the TPS and re-check.
2. Check for an intermittent open or short in the TPS signal. To do that, you can't use a scan tool. You'll need an oscilliscope. The reason is because scan tools take samplings of many different readings over just one or two data lines and can miss an intermittent drop out. Hook up your oscilliscope and watch the signal. It should sweep up and down smoothly with no drop outs or spikes.
3. If no problems were noticed, perform a wiggle test. Do this by wiggling the connector and harness while watching the pattern. Does it drop out? If so, replace TPS and re-check.
4. If you have no TPS signal, check for 5 Volt reference at the connector. If it's present, check the ground circuit for open or shorts.
5. Make sure the signal circuit isn't 12V. It should never have battery voltage. If it does, trace circuit for short to voltage and repair.
6. Look for any water in the connector and replace TPS as necessary

your transmission is in "limp home" mode, the problem is one of the sensors on your transmission. you need to have an obdII scanner connected to read the codes stored in your vehicles computer. this will tell you which sensor has failed

take it to auto zone have them run there free test and see what is going on.

Keith Heavilin had the right answer to the problem. Thanks again Keith!!! When i ran a scan on the jeep it came up po123, which is tps sig input a high. Keith told me to replace the clock spring and now it is fixed. He said this is a common problem on jeep grand cherokees. i wish i would have known this before i spent 100$ on a tps unit