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P0123 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

This code represents a malfunction in the Throttle Pedal Position Sensor/Switch (TPS). It indicates that circuit A has a high voltage input. It is a powertrain code relating to an issue with fuel and air metering.

Meaning

P0123 is a generic 0BD-II code. It indicates that the Engine Control Module (ECM) found a problem with the Throttle Pedal Position Sensor/Switch (TPS), which is mounted to the throttle body on the top of the engine. The A circuit output voltage has exceeded the sensor’s expected voltage specification range. 

The TPS monitors the air intake of the engine by responding to the movement of the accelerator pedal. The Engine Control Module (ECM) uses the measured voltage for emission control, including the air-fuel ratio and spark timing.

Causes

The malfunction gets triggered when the TPS circuit A range output to the ECM exceeds 4.54 volts for more than two seconds. When this occurs, it could indicate a problem with the TPS itself without any further issue. Perhaps it is not mounted correctly or needs replacing.

Other causes include faulty TPS wiring/connections or a dirty throttle body. A carbon buildup in the throttle body will also cause this malfunction. 

Symptoms

When this malfunction occurs the Check Engine Light comes on and the ECM enters failsafe mode. The ECM will cut the current to the throttle actuator, causing the throttle valve to close to less than six degrees of plate opening. 

The ECM will control engine speeds by altering fuel injection and timing. The exact symptoms vary depending on the make and model of the vehicle. However, expect difficulty starting, higher idles and a decreased acceleration response.

The vehicle can still drive, but very slowly and with a limited throttle response.  

Diagnosis

Verify the malfunction by performing a scan and documenting the arising codes. The freeze frame data from the scan indicates when the code was set.

Then, clear the OBD-II fault codes and perform another test to double check if the codes come back. 

After confirming the presence of a malfunction, check the TPS connections and wiring for shorting and damages. Since faulty wiring often causes the problem, it may extend no further than a bad connection.

Repair any wiring or connection shorts, but continue examining data from the scanner to ensure total resolution of the malfunction.

Compare the data between TPS circuits A and B on the scanner. If finding a discrepancy between the data points, perform the TPS pinpoint tests as per the vehicle manufacturer’s recommendations.

Finally, replace the TPS as specified by the pinpoint test and clear the codes from the scanner. Test the vehicle on the road to make sure everything feels right and the symptoms are gone. 

Common mistakes

While attempting to solve the P0123 code, many fail to visually inspect the wiring and connections first. These problems cause the majority of P0123 codes, so checking the connections first could save a lot of hassle.

Be sure to scan, document and clear once, then repeat the test again. Verifying the failure ensures an appropriate correction of the malfunction.

After replacing the sensor, repair and verify any connection issues. Double check a complete connection after performing your tests.

Many replace the TPS sensor without making sure it caused the problem. To avoid this mistake, verify that the A and B circuit voltages are within specifications before and after repairs. If you replace the TPS, double check the voltage again to make sure it works.

How serious is this?

Since the ECM goes into failsafe mode when the P0123 code arises, various operation issues will occur until repairs are made. Stalling, poor acceleration, bucking/jerking, higher idles and limited speeds could result from the code malfunction.

To ensure your safety and the safety of other drivers, solve the problem as soon as possible.

What repairs can fix the code?

P0123 is relatively easy to fix. The code can be fixed by repairing or replacing the TPS wiring and/or connections. 

In the case of a faulty TPS sensor, replace this part to solve the issue. Just make sure you double check the connections and perform a voltage test of the circuits so that you do not have to backtrack and start over again.

Related codes

Some related codes include  P0121, P0122 and P0124

Conclusion

Whenever an issue arises with your engine, it is important to fix it as soon as possible. In the case of the P0123 code, engine performance will suffer greatly. While the specific problems vary depending on the vehicle, the ECM goes into failsafe mode which needs to be corrected.

Follow the above steps to diagnose the malfunction and solve it with relative ease.

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