Symptoms

Potential symptoms include:

• MIL (Malfunction Indicator Lamp) illumination
• Misfires at idle or highway speed
• Poor idle quality
• May not idle
• May start and stall

Causes

Potential causes of P2120 code include:

1. Sticking throttle return spring
2. Corrosion of MAP or TPS connectors
3. Misrouted harness causing chafing
4. Faulty TPS
5. Faulty PCM

Possible Solutions

If you have access to a scan tool, with KOEO (Key On Engine Off), monitor TPS voltage. With the throttle closed, voltage should be approximately 0.45 volts. It should gradually sweep upward to about 4.5 to 5 volts as you press the accelerator. Sometimes only an oscilloscope can capture an intermittent problem in the TPS signal voltage. If you notice an issue in the TPS sweep voltage, replace the TPS.

NOTE: Some TPS sensors require fine adjustment. If you are not comfortable using a DVOM (Digital Volt Ohm Meter) to adjust the new TPS, then it is best to take the vehicle to a shop. If the voltage is not 0.45 volts (+ or – approximately 0.3 volts) with the throttle closed or if the reading is “stuck,” disconnect the TPS connector. With KOEO, check for the 5-volt reference voltage present at the connector and a good ground. You can check the signal circuit continuity by jumpering a fuse wire between the TPS connector ground circuit and the signal circuit. If the TPS reading on the scan tool now reads zero, replace the TPS. However, if it does not change the reading to zero, check for an open or short in the signal wire and if none is found, suspect a faulty PCM. If manipulating the TPS wiring harness causes a change at idle, suspect a faulty TPS.

Symptoms

Potential

Symptoms of a P2121 trouble code may include:

• Illumination of the Malfunction Indicator Lamp (MIL) (Check Engine Light or Service Engine Soon light)
• Intermittent stumbling during acceleration or deceleration
• Black smoke puff during acceleration
• No start condition

Causes

A P2121 code may indicate that one or more of the following events has occurred:

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

Possible Solutions

1. If you have access to a scan tool, check the idle and WOT (wide open throttle) readings for the TPS. Verify if they are close to the specifications mentioned above. If not, replace the TPS and recheck.

2. Look for an intermittent open or short in the TPS signal. To do this, you cannot use a scan tool. You will need an oscilloscope. The reason is that scan tools sample many different readings over one or two data lines and may miss an intermittent interruption. Connect your oscilloscope and observe the signal. It should sweep up and down smoothly without jerks or spikes.

3. If no issue was found, perform a wiggle test. To do this, wiggle the connector and harness while observing the pattern. Does it stop? If yes, replace the TPS and recheck.

4. If you have no TPS signal, check for the 5-volt reference at the connector. If present, check if the ground circuit is open or shorted.

5. Ensure the signal circuit is not at 12V. It should never have battery voltage. If it does, trace the circuit for a short and repair.

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

Symptoms

Symptoms may include:

• Irregular or low idle
• Stalling
• Surging
• No/little acceleration
• Other symptoms may also be present

Causes

A P2122 code may mean one or more of the following has occurred:

1. TPS not securely mounted
2. Short circuit in TPS wiring to ground or another wire
3. Faulty TPS
4. Damaged computer (PCM)

Possible Solutions

Here are some recommended troubleshooting and repair steps:

Carefully inspect the throttle position sensor (TPS), wiring connector, and wiring for breaks, etc. Repair or replace if necessary
Check voltage at TPS (refer to your vehicle’s service manual for specific information). If voltage is too low, this indicates a problem. Replace if necessary.
If recently replaced, the TPS may need adjustment. On some vehicles, installation instructions require proper TPS alignment or adjustment, consult a repair manual for details.
If there are no symptoms, the problem may be intermittent and clearing the code may temporarily resolve the issue. If this is the case, you should definitely check wiring to ensure it’s not rubbing against anything, grounding, etc. The code may return.

Symptoms / Severity

When this code is stored, the PCM typically enters limp mode. Engine acceleration will be severely limited (if not disabled) in this mode. Symptoms of a P2123 code may include:

• Stuck accelerator (at any RPM)
• Limited or no acceleration
• Engine stalling at idle
• Hesitation during acceleration
• Inoperative cruise control

Causes

Possible causes of this engine code include:

• Open or shorted circuits between the TPS, PPS, and PCM
• Faulty TPS or PPS
• Corroded electrical connectors
• Faulty cable actuator motor

Diagnostic and Repair Procedures

A good starting point is always to check the technical service bulletins (TSB) for your specific vehicle. Your issue might be a known problem with a published manufacturer fix, which can save you time and money during diagnosis.

I would use a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a vehicle information source like All Data (DIY) to diagnose a P2123 code.

I would begin my diagnosis with a visual inspection of all cables and connectors related to the system. I also like to check the throttle plate for signs of carbon buildup or damage. Excessive carbon buildup, which keeps the throttle body open at startup, can cause a P2123 code to be stored. Clean the carbon from the throttle body according to manufacturer recommendations and repair or replace any faulty wiring or components as needed, then retest the DBW system.

Next, I connect the scanner to the vehicle’s diagnostic port and retrieve all stored trouble codes. I note them down in case I need the order in which the codes were stored. I also like to save all related freeze frame data. These notes can prove useful if the P2123 turns out to be intermittent. Now, I clear the codes and test the vehicle. If the code resets, I continue my diagnosis.

Voltage spikes and inconsistencies between the TPS, PPS, and PCM can be detected using the scanner’s data stream. Narrow the data stream to display only relevant data for a faster response. If no spikes and/or inconsistencies are detected, use the DVOM to retrieve live data from each sensor individually. To retrieve live data with the DVOM, connect the test leads to the appropriate signal and ground circuits and observe the DVOM display while operating the DBW. Look for voltage spikes when the accelerator is slowly moved from the closed position to wide-open throttle. Voltage typically ranges from 0.5 volts at closed throttle to 4.5 volts at wide-open throttle. If spikes or other irregularities are detected, suspect that the tested sensor is faulty. An oscilloscope is also an excellent tool for testing sensor operation.

Additional Diagnostic Notes:

Some manufacturers require that the throttle body, throttle actuator motor, and all throttle position sensors be replaced together.

Severity and Symptoms

The TPS plays an important role in engine operation, therefore, a stored P2124 code should be treated with a certain degree of urgency.

Symptoms of a P2124 code may include:

• Hesitation during acceleration
• Black smoke from engine exhaust (especially at startup)
• Delayed engine starting (particularly during cold starts)
• Reduced fuel efficiency
• Stored emission-related codes may accompany a P2124

Possible causes of this engine code include:

• Faulty or improperly adjusted TPS
• Open or shorted TPS “D” wires or connectors
• Binding or damaged throttle plate
• Incorrect PCM or PCM programming error

Diagnostic and Repair Procedures

A good starting point is always to check the Technical Service Bulletins (TSBs) for your specific vehicle. Your issue may be a known problem with a known fix published by the manufacturer and can save you time and money during diagnosis.

I typically use a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle information source (ALL DATA DIY) to diagnose a P2124 code.

Successful diagnosis usually begins with a visual inspection of all cables and connectors related to the system. I also like to test the throttle plate for signs of coking or carbon damage. Repair or replace faulty wiring or components as needed, then recheck the throttle body and TPS.

Connect the scanner to the diagnostic connector; retrieve all stored fault codes and note them for future reference. I also keep all associated freeze frame data. My notes are often helpful if the stored code proves to be intermittent. Then I would clear the codes and test the vehicle. Continue diagnosis if the code resets. If it doesn’t reset, the condition may need to worsen before a proper diagnosis can be made. Drive the vehicle normally until the PCM enters readiness mode or the code resets.

Proceed by checking the Technical Service Bulletins (TSBs) that apply to the specific malfunction (and vehicle) in question by consulting your vehicle information source. If applicable, use the information in the appropriate TSB to assist in your diagnosis. TSBs can be particularly helpful when diagnosing an intermittent condition.

The scanner data stream can provide useful information regarding faults and inconsistencies in the throttle position sensor. If you filter the scanner data stream to display only relevant data, you’ll get a more accurate response from the data.

If no issues are detected, use the DVOM to test the TPS. Using the DVOM gives you access to live data if the appropriate test leads are connected to the ground and signal circuits. Watch the DVOM screen while manually operating the throttle. Look for voltage spikes when the throttle is slowly operated from closed position to wide open throttle. Voltage typically ranges from 0.5 volts at closed throttle to 4.5 volts at open throttle. If faults or other inconsistencies are detected, suspect that the tested sensor is faulty or improperly adjusted.

Additional Diagnostic Notes:

If the TPS has been replaced and a P2124 continues to be stored, consult the vehicle information source for TPS adjustment specifications
Use the DVOM (with test leads connected to ground and signal circuits) to accurately adjust the TPS

Technical Definition

Code P2125 indicates a problem with the performance or signal range in the throttle position sensor (TPS) circuit. This sensor measures the throttle opening angle and sends a signal to the PCM (Powertrain Control Module) to regulate fuel injection and ignition. An incorrect signal disrupts the air-fuel mixture, affecting engine performance.

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Common Symptoms

• Check engine light on (MIL).
• Unstable idle or vibrations.
• Misfires during acceleration or at constant speed.
• Hard starting or engine stalling.
• Noticeable power loss.

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Main Causes

Category	Details
Mechanical issues	Sticking or binding throttle return spring.
Electrical failures	Damaged wiring, corroded MAP/TPS connectors, short circuit.
Faulty TPS sensor	Inconsistent signal or voltage range interruption.
Failing PCM	Incorrect interpretation of TPS signal.

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Diagnostic Steps

1. Check TPS Voltage (KOEO)

• Tool required: Digital multimeter (DVOM) or oscilloscope.
• Procedure:
  1. Turn ignition on (without starting the engine).
  2. Measure voltage between the signal wire and ground.
  3. Expected values:
     • Throttle closed: ~0.45 V (tolerance ±0.3 V).
     • Throttle open: ~4.5–5 V.

2. Test Electrical Circuit

• Continuity: Check for no breaks between TPS and PCM.
• 5V Reference: With TPS connector unplugged, ensure reference wire provides 5V.
• Ground: Test ground connection with ohmmeter (< 1 Ω).

3. Inspect Wiring and Connectors

• Chafing/Corrosion: Look for frayed wires or greenish connectors.
• Harness manipulation: Gently shake TPS wiring during measurement to detect intermittent issues.

4. Diagnose PCM

• Signal simulation: Short signal wire to ground. If voltage remains stuck, suspect faulty PCM.

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Solutions and Costs

Problem	Solution	Estimated Cost (€)
Faulty TPS sensor	Replace and recalibrate (e.g., Bosch 0280126004).	50–150
Damaged wiring	Repair harness or replace connector.	30–200
Throttle cleaning	Remove and clean with specific degreaser.	20–80
PCM replacement	Reprogramming or exchange at dealership.	500–1,500

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Best Practices

• TPS calibration: After replacement, adjust voltage to 0.45 V with throttle closed (follow manufacturer’s manual).
• Use an oscilloscope: To capture intermittent issues not visible with a multimeter.

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FAQ

Q: Can I drive with a P2125 code?
A: Yes, but avoid sudden acceleration. The engine may stall or consume more fuel.

Q: The code returns after replacing the TPS. Why?
A: Check wiring or PCM. Residual short circuit or incorrect calibration may persist.

Symptoms

Potential

Symptoms of a P2126 trouble code may include:

• Illumination of the Malfunction Indicator Lamp (MIL) (Check Engine light or Service Engine Soon light)
• Intermittent stumbling during acceleration or deceleration
• Black smoke puff during acceleration
• No start condition

Causes

A P2126 code may indicate that one or more of the following events has occurred:

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

Possible Solutions

1. If you have access to a scan tool, check the idle and WOT (wide open throttle) readings for the TPS. Verify if they are close to the specifications mentioned above. If not, replace the TPS and recheck.

2. Look for an intermittent open or short in the TPS signal. To do this, you cannot use a scan tool. You will need an oscilloscope. The reason is that scan tools sample many different readings over one or two data lines and may miss an intermittent interruption. Connect your oscilloscope and observe the signal. It should sweep smoothly up and down without jerks or spikes.

3. If no issues were found, perform a wiggle test. To do this, wiggle the connector and harness while observing the pattern. Does it drop out? If yes, replace the TPS and recheck.

4. If you have no TPS signal, check for the 5-volt reference at the connector. If present, check if the ground circuit is open or shorted.

5. Ensure the signal circuit is not at 12V. It should never have battery voltage. If it does, trace the circuit for a short and repair.

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

Symptoms

Symptoms may include:

• Irregular or low idle
• Stalling
• Surging
• No/little acceleration
• Other symptoms may also be present

Causes

A P2127 code may mean that one or more of the following events have occurred:

• TPS not securely mounted
• Short circuit of TPS circuit to ground or another wire
• Faulty TPS
• Damaged computer (PCM)

Possible Solutions

Here are some recommended troubleshooting and repair steps:

Carefully check the throttle position sensor (TPS), wiring connector, and wiring for breaks, etc. Repair or replace if necessary
Check the voltage at the TPS (refer to your vehicle’s maintenance manual for specific information). If the voltage is too low, it indicates a problem. Replace if necessary.
If it has been recently replaced, the TPS may need to be adjusted. On some vehicles, installation instructions require the TPS to be properly aligned or adjusted, consult a repair manual for details.
If there are no symptoms, the problem may be intermittent and clearing the code may temporarily resolve the issue. If this is the case, you should definitely check the wiring to ensure it is not rubbing against anything, grounding, etc. The code may return.

Code P2128: Causes, Repairs, and Symptoms

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What does code P2128 mean?

The Powertrain Control Module (PCM) detects an anomaly in the signals from the Throttle Position Sensor (TPS) or the Pedal Position Sensor (PPS). This code is stored when the values from these sensors are inconsistent or out of range, forcing the PCM to activate a limp mode (“limp home mode”), drastically limiting engine performance.

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Possible causes of code P2128

1. Electrical faults:

• Short circuit or open circuit between the TPS, PPS, and PCM.
• Damaged wires or degraded insulation.

1. Faulty sensors:

• Defective TPS or PPS (erratic signal or no signal).

1. Connection problems:

• Corroded, oxidized, or poorly secured connectors.

1. Mechanical failure:

• Failed throttle actuator motor.
• Carbon buildup blocking the throttle body.

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Symptoms and severity of code P2128

• Limp mode activated:
• Severely limited or disabled acceleration.
• Reduced engine power to prevent damage.
• Driving problems:
• Throttle stuck at a fixed RPM.
• Engine stalling at idle.
• Hesitation or no response to acceleration.
• Cruise control inoperative.
• Severity: High – Risk of vehicle immobilization or complete breakdown.

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Diagnostic and repair procedures

1. Check Technical Service Bulletins (TSBs):

• Look for manufacturer fixes for your model.

1. Visual inspection:

• Check cables, connectors, and the throttle body (clean carbon if necessary).

1. Electronic diagnosis:

• OBD2 scanner: Read codes and analyze data stream (TPS/PPS).
• Multimeter/oscilloscope:
  • Measure sensor voltage (0.5 V at closed throttle → 4.5 V at open throttle).
  • Identify voltage spikes or irregular signals.

1. In-depth electrical tests:

• Check circuit continuity and resistance.
• Look for short circuits to ground or overvoltages.

1. Component replacement:

• Replace the TPS, PPS, or actuator if faulty.
• Note: Some manufacturers require replacing the entire throttle body with its sensors.

Tip: After repair, reset the PCM and perform a road test to verify that the symptoms have disappeared.

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Additional technical information

• Sensor locations:
• TPS: Integrated into the throttle body.
• PPS: Located on the accelerator pedal.
• Impact of an unresolved fault:
• Premature engine wear, increased fuel consumption, polluting emissions.
• Recommended tool: Oscilloscope to precisely visualize sensor signals.

For complex Drive-by-Wire systems, prefer intervention by a professional equipped with specific tools.

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Reference: Always prioritize diagnosing main codes before associated codes.

Severity and Symptoms

The TPS plays an important role in engine operation, so a stored P2129 code should be addressed with a certain degree of urgency.

Symptoms of a P2129 code may include:

• Hesitation during acceleration
• Black smoke from engine exhaust (particularly at startup)
• Delayed engine starting (especially during a cold start)
• Reduced fuel efficiency
• Related stored emission codes may accompany a P2129

Causes

Possible causes of this engine code include:

• Faulty or improperly adjusted TPS
• Open or shorted TPS “E” wires or connectors
• Binding or damaged throttle plate
• Incorrect PCM or PCM programming error

Diagnostic and Repair Procedures

A good starting point is always to check the Technical Service Bulletins (TSBs) for your specific vehicle. Your issue might be a known problem with a published fix from the manufacturer, which can save you time and money during diagnosis.

I typically use a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle information source (like ALLDATA DIY) to diagnose a P2129 code.

Successful diagnosis usually begins with a visual inspection of all wiring and connectors related to the system. I also like to test the throttle plate for signs of coking or carbon damage. Repair or replace any faulty wiring or components as needed, then recheck the throttle body and TPS.

Connect the scanner to the diagnostic connector; retrieve all stored fault codes and note them for future reference. I also save any associated freeze frame data. My notes often prove useful if the stored code turns out to be intermittent. Then, I would clear the codes and test drive the vehicle. Continue diagnostics if the code resets. If it doesn’t reset, the condition might need to worsen before a proper diagnosis can be made. Drive the vehicle normally until the PCM enters readiness mode or the code resets.

Proceed by checking the Technical Service Bulletins (TSBs) that apply to the specific malfunction (and vehicle) in question by consulting your vehicle information source. If applicable, use the information in the relevant TSB to aid your diagnosis. TSBs can be particularly helpful when diagnosing an intermittent condition.

The scanner data stream can provide useful information regarding faults and inconsistencies in the throttle position sensor. If you filter the scanner data stream to display only relevant data, you’ll get a more accurate response from the data.

If no issues are detected, use the DVOM to test the TPS. Using the DVOM gives you access to live data if the appropriate test leads are connected to the ground and signal circuits. Watch the DVOM screen while manually operating the throttle. Look for voltage spikes when the throttle is slowly moved from the closed position to wide open throttle. Voltage typically ranges from 0.5 volts at closed throttle to 4.5 volts at open throttle. If faults or other inconsistencies are detected, suspect that the tested sensor is faulty or improperly adjusted.

Additional Diagnostic Notes:

• If the TPS has been replaced and a P2129 continues to be stored, consult the vehicle information source for TPS adjustment specifications
• Use the DVOM (with test leads connected to the ground and signal circuits) to accurately adjust the TPS