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P0122 means the TPS signal is stuck near 0V or well below the 0.5V closed-throttle minimum. Check the TPS ground wire first - a broken ground pulls the signal low without any sensor fault. Inspect the connector for spread pins or corrosion before replacing parts. See top-rated scanners on Amazon ↗
🗺️ Where Is the Problem?
Blueprint view - P0122 fault: TPS signal voltage below 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 P0122 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 Ground
A wiring short between the TPS signal wire and a ground path pulls the signal voltage to near zero. This is the leading cause of P0122. Inspect the wiring harness for pinched, chafed, or melted insulation along the entire length from the TPS to the PCM connector.
🔩 Part
$5–$30
👨🔧 Labor
$60–$150
⚡ DIY Difficulty
Medium
40%
#2 - Check First
Failed TPS at Minimum Rotation
The TPS internal resistive element has failed at the closed-throttle end of its travel, outputting a voltage below 0.2V when the PCM expects at least 0.5V. This requires TPS replacement. Confirm by measuring voltage at the TPS connector while wiggling the sensor.
🔩 Part
$30–$120
👨🔧 Labor
$40–$100
⚡ DIY Difficulty
Easy
12%
#3 - Less Common
Damaged Wiring to TPS
A broken or high-resistance connection in the signal wire - often caused by a bad connector, pulled terminal, or heat-damaged wire - reduces signal voltage. Use a DVOM to check for more than 0.5 ohms resistance in the signal wire with the connector disconnected.
🔩 Part
$5–$40
👨🔧 Labor
$60–$150
⚡ DIY Difficulty
Medium
3%
#4 -
Dirty Throttle Body
Extreme carbon buildup can cause the throttle plate to sit in an abnormal closed position, affecting the mechanical stop and making the TPS read lower than expected. Clean the throttle body and verify idle position before condemning any electrical components.
🔩 Part
$5–$15
👨🔧 Labor
$0–$60
⚡ DIY Difficulty
Easy
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Check TPS Signal Voltage at Idle - With the key on, engine off, measure voltage at the TPS signal wire (center pin on most 3-wire sensors). It should read 0.4–0.6V at closed throttle. Below 0.2V confirms P0122 territory - check for a short to ground next.
- Inspect Wiring for Short to Ground - Unplug the TPS connector and check resistance between the signal wire and ground. Less than 10k ohms indicates a short to ground somewhere in the harness. Trace the harness for chafed insulation or pinch points.
📍 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