What Does P0122 Mean?
The ECM has detected that the throttle position sensor A circuit voltage is below the minimum expected threshold, typically below 0.2V. This indicates a short to ground in the TPS signal circuit, a failed sensor with a grounded wiper, or a loss of the 5V reference supply to the sensor. The ECM will typically enter reduced power mode to protect against unintended acceleration.
Common Causes
35%
Failed TPS with internally shorted signal element or grounded wiper contact
25%
Short to ground in TPS signal wire caused by chafing against engine bracket or intake manifold bolt
20%
Loss of 5V reference supply to TPS due to shorted sensor on the shared 5V reference bus
20%
Corroded or water-damaged TPS connector causing signal to be pulled low through moisture bridging
Diagnostic Steps
1
With the key on and engine off, check TPS A voltage on a scan tool. If reading 0V or near 0V, the signal is shorted to ground. Disconnect the TPS connector and recheck; if voltage rises to near 5V at the ECM, the fault is in the sensor.
2
Verify the 5V reference voltage is present at the TPS connector. If the 5V reference is missing or low, disconnect other sensors sharing the same 5V reference bus (MAP, fuel pressure, oil pressure) one at a time to find the shorting sensor.
3
Inspect the TPS signal wire routing for chafing points, especially where the harness passes near sharp metal edges, exhaust components, or mounting bolts.
4
Check the TPS connector for moisture intrusion, corrosion, or green deposits on terminals. Clean with electronic contact cleaner and apply dielectric grease before reassembly.
5
If the TPS is integrated into the electronic throttle body, the entire throttle body assembly may need replacement as the sensor is not serviceable separately on most modern vehicles.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
The ECM has detected that the throttle position sensor A circuit voltage is below the minimum expected threshold, typically below 0.2V. This indicates a short to ground in the TPS signal circuit, a failed sensor with a grounded wiper, or a loss of the 5V reference supply to the sensor. The ECM will ...
The most common cause of P0122 (Throttle/Pedal Position Sensor/Switch A Circuit Low Input) is: Failed TPS with internally shorted signal element or grounded wiper contact
Typical repair costs for P0122 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A low TPS signal causes the ECM to see the throttle as fully closed regardless of actual position. This triggers reduced power mode and may cause the engine to stall or be unable to accelerate, creating a dangerous situation in traffic.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0122 to identify the root cause.
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Quick Info
Category
Powertrain
System
Electronic Throttle Control System
Difficulty
Type
Generic (SAE)
Recommended Tools
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