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P0123 means TPS signal is stuck near 5V (maximum) or above the 4.8V WOT ceiling. The PCM sees a wide-open throttle signal even at idle, causing over-fueling and unsafe throttle behavior. Check for a short to the 5V reference wire before replacing the TPS. See top-rated scanners on Amazon ↗
🗺️ Where Is the Problem?
Blueprint view - P0123 fault: TPS signal voltage above threshold, throttle body area
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0123 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
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🎯 Top Causes & Probability
45%
#1 - Most Likely
TPS Circuit Short to Voltage
A wiring short between the TPS signal wire and the 5V reference wire (or any other voltage source) drives the signal above the 4.8V maximum. This is the most common cause of P0123. Inspect harness routing for areas where wires may contact each other or a power source.
🔩 Part
$5–$30
👨🔧 Labor
$60–$150
⚡ DIY Difficulty
Medium
40%
#2 - Check First
Failed TPS at Maximum Position
The TPS sensor's internal resistive track has failed at the wide-open-throttle end, outputting maximum voltage even at idle. A scan tool will show TPS % reading at 90–100% with the throttle closed. Replace the TPS sensor - OEM fitment is recommended for drive-by-wire vehicles.
🔩 Part
$30–$120
👨🔧 Labor
$40–$100
⚡ DIY Difficulty
Easy
12%
#3 - Less Common
Wiring Chafing on Positive Source
Chafed wiring where the TPS signal wire routes near a battery positive cable or ignition feed can create an intermittent short to power. The code may set only under certain driving conditions or vibration. A careful harness inspection under the hood and firewall is needed.
🔩 Part
$5–$30
👨🔧 Labor
$60–$150
⚡ DIY Difficulty
Medium
3%
#4 -
Contaminated TPS Track
Oil, coolant, or water intrusion inside the TPS sensor body can contaminate the resistive track, causing a high-resistance jump at certain positions that reads as high voltage. Inspect the TPS body and connector for signs of fluid intrusion - look for corrosion or deposits inside the connector.
🔩 Part
$30–$120
👨🔧 Labor
$40–$100
⚡ DIY Difficulty
Easy
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Verify TPS Voltage at Idle - With key on, engine off, probe the TPS signal wire. Any reading above 4.8V at closed throttle confirms P0123 territory. A reading near 5V suggests a short to the reference voltage wire.
- Disconnect TPS and Recheck Signal Wire - Unplug the TPS connector and re-measure voltage on the signal wire (harness side). If voltage is still near 5V with the sensor disconnected, you have a wiring short to power - not a sensor fault.
📍 Find a Trusted Shop Near You
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Tips for Choosing a Shop
- Ask if they charge a diagnostic fee and whether it applies toward the repair
- Request a written estimate before approving any work
- Ask specifically about the part brand - OEM vs. aftermarket matters for this code
- Check Google reviews for recent mentions of the specific repair you need