Fix P0123: Mechanic’s solutions that WORKED

The code P0123: Throttle/Pedal Position Sensor/Switch “A” Circuit High Input indicates a problem with the throttle position sensor, where the input signal to the engine’s control system is registering too high. This issue is commonly caused by a faulty sensor, wiring problems, or malfunctions in the engine’s control unit.

P0123 quick overview

Meaning	P0123: Throttle/Pedal Position Sensor/Switch “A” Circuit High Input
Is it serious?	Yes, it can affect the vehicle’s drivability and fuel efficiency, potentially causing erratic throttle response or idle issues.
Possible causes	– Faulty throttle position sensor (TPS) – Wiring or connector issues related to the TPS – Problems with the Powertrain Control Module (PCM) or Engine Control Module (ECM) – Vacuum leaks in the intake system – Short circuits or electrical disturbances in related systems (e.g., clockspring)
How to diagnose?	Inspect TPS: Check the throttle position sensor for damage or malfunction. Check Wiring and Connectors: Examine the wiring and connectors leading to the TPS for any signs of damage or corrosion. Test Voltage at TPS and ECM: Perform voltage tests at the TPS and ECM to ensure proper readings. Evaluate PCM/ECM: Consider potential issues with the PCM or ECM, especially if there have been recent replacements. Look for Vacuum Leaks: Inspect the intake manifold and related components for any vacuum leaks. Check Related Systems: Examine systems that might influence the TPS circuit, such as clockspring or cruise control.

In simpler terms, the P0123 code means that the sensor which tells your car’s computer how far the gas pedal is pressed is sending a signal that’s too high. This could make your car’s engine behave unpredictably or use more fuel than it should. It’s often due to a sensor issue, but it could also be a wiring problem or something wrong with the car’s computer itself.

How to fix P0123 – learn from mechanics

I looked into P0123 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Mazda

Vehicle Information

• 1999 Mazda Miata 10th Anniversary 1.8L

Issue + Repair History

• MIL Lamp on.
• Code: P0123A (TPS too high).

Computer Codes & Descriptions

• P0123A – TPS too high

Suggestions to Fix Issue

• Adjust the TPS sensor between 500mv to 800 mv.
• Consider the possibility of a MAF sensor malfunction.
• Measure the voltage on the TPS to check if it’s too high.
• Assess if the TPS is adjustable and if the base idle is correct.

Final Fix

• Replaced the throttle position sensor (TPS).
• Cleaned the MAF sensor wire.
• Resolved the issue, and the MIL turned off.

Case #2: Jeep

Vehicle Information

• 1998 Jeep Wrangler SE 2.5L

Issue + Repair History

• MIL Lamp on.
• Code: P0123 (TPS high).
• Scans at 4.84v with closed throttle (should be around 1.0v).
• PCM replacement after a wreck.
• Found signal of 1.07v at PCM with good connector.
• Power and grounds checked and are okay at PCM.

Computer Codes & Descriptions

• P0123 – TPS high

Other Test Results

• TPS reference voltage at 5.11v
• Ground within 0.50mV
• Voltage drop, grounds, power at PCM – OK, less than 25mV

Suggestions to Fix Issue

• Consider the possibility of an issue with the clockspring.

Final Fix

• Disconnected the horn/cruise connector, bringing TPS scan voltage to normal (0.78v).
• Replaced the clockspring to complete the repair.

Case #3: Dodge

Vehicle Information

• 1997 Dodge Dakota 2.5L

Issue + Repair History

• Poor idle quality, poor fuel economy, MIL Lamp on.
• Code: P0123 (TP fixed above 4.7 volts).
• TP sensor ground OK, 5V reference OK at TP, but sense wire at TP also shows 5V.
• Wire from TP sensor reads 0.65V (normal), but ECM terminal shows 5V.
• ECM replaced at another shop for the same problem, which did not resolve the issue.

Computer Codes & Descriptions

• P0123 – TP fixed above 4.7 volts

Suggestions to Fix Issue

• Check for a short to voltage inside the clockspring, as it can affect the TPS circuit.
• Disconnect the clockspring and see if the code disappears.
• Check continuity of TP signal wire and 5V reference wire for potential shorts.

Final Fix

• The problem was a short to voltage inside the clockspring.
• Resolving the issue with the clockspring corrected the TP sensor reading.

Case #4: Chevrolet

Vehicle Information

• 1996 Chevrolet C3500 5.7L

Issue + Repair History

• Intermittent issues: stalling on deceleration, high idle on deceleration, and MIL Lamp on.
• Codes: P1122, P0122, and P0123 (all related to TPS).
• Recent repairs: Replaced fuel tank module and EGR valve.
• TPS and harness pigtail replaced without improvement.

Computer Codes & Descriptions

• P0123 – TPS
• P0122 – TPS
• P1122 – TPS

Other Test Results

• TPS scan and fuel pressure: Good

Suggestions to Fix Issue

• Check ground circuits for bad connections.
• Consider the possibility of the ECM losing internal ground for the TPS.

Final Fix

• Replaced the ECM, which resolved the problem.

Case #5: BMW

Vehicle Information

• 2013 BMW ActiveHybrid 3 3.0L

Issue + Repair History

• MIL Lamp on, Auto Start/Stop disabled message on cluster.
• Code: P123B (only on the generic side, no manufacturer-side codes).
• Auto Start/Stop functions a few times after clearing the code, then disables and flags P123B code again.

Suggestions to Fix Issue

• Conduct a full scan and read all control units.
• Test the battery and charging system, as issues here can disable Auto Start/Stop.
• Check battery state-of-charge and state-of-health.
• Look for low-voltage codes and U-codes during a complete vehicle scan.
• Consider the age and condition of the OEM 12-volt battery, as it can affect system performance.

Final Fix

• Found that the electric vacuum pump was not activating, causing the Electric Machine Electronics (EME) module to start the engine for booster vacuum.
• Discovered a TSB for vacuum pump failure with extended warranty coverage.
• Had the vacuum pump fixed at the dealer under warranty.
• Problem solved, though the code definition was never found.

Advice	Diagnostic Step Description
Check Throttle Position Sensor (TPS)	Inspect the TPS for proper operation and correct voltage readings.
Inspect Wiring and Connectors	Check the wiring and connectors for damage or corrosion, especially at the TPS.
Evaluate PCM/ECM Functionality	Consider the possibility of PCM/ECM issues, especially if replacements didn’t resolve the problem.
Perform Voltage Tests	Conduct voltage tests at the TPS and ECM to identify discrepancies.
Check for Vacuum Leaks	Inspect the intake manifold and associated components for vacuum leaks.
Inspect Related Components	Check related components like the clockspring or cruise control circuit, as they may influence TPS readings.
Verify Sensor Calibration	Ensure the TPS is properly calibrated and within specified voltage range.