What Does P0123 Mean?
The ECM has detected that the throttle position sensor A circuit voltage exceeds the maximum expected threshold, typically above 4.8V. This indicates an open ground circuit, a short to voltage on the signal wire, or a failed sensor with the signal stuck high. The ECM interprets this as the throttle being wide open and will typically enter reduced power mode or shut down fueling to prevent engine runaway.
Common Causes
35%
Failed TPS with open internal ground path causing signal to float up to reference voltage
25%
Open or high-resistance ground wire in TPS circuit preventing proper voltage divider operation
20%
TPS signal wire shorted to the 5V reference wire or battery voltage through harness damage
20%
Corroded or disconnected TPS ground terminal at the sensor connector
Diagnostic Steps
1
With key on engine off, check TPS A voltage on a scan tool. If reading above 4.8V, disconnect the TPS connector. If voltage drops to near 0V at the ECM harness side, the sensor is faulty.
2
With the TPS disconnected, check for 5V reference and ground at the harness-side connector. If ground is missing or shows high resistance (above 5 ohms), trace and repair the ground circuit.
3
Check for shorts between the TPS signal wire and the 5V reference wire by measuring resistance between the two pins at the ECM connector with the TPS disconnected. They should not be connected.
4
Inspect the TPS connector for backed-out ground terminal, corrosion on the ground pin, or a broken ground wire at the crimp terminal.
5
If the issue is intermittent, wiggle the TPS connector and harness while monitoring voltage on a scan tool to isolate the point of failure.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
The ECM has detected that the throttle position sensor A circuit voltage exceeds the maximum expected threshold, typically above 4.8V. This indicates an open ground circuit, a short to voltage on the signal wire, or a failed sensor with the signal stuck high. The ECM interprets this as the throttle ...
The most common cause of P0123 (Throttle/Pedal Position Sensor/Switch A Circuit High Input) is: Failed TPS with open internal ground path causing signal to float up to reference voltage
Typical repair costs for P0123 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A stuck-high TPS signal makes the ECM believe the throttle is wide open, which triggers immediate fuel cutoff and reduced power mode. The vehicle may stall unexpectedly or refuse to accelerate, creating hazardous situations on roadways.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0123 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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