📋 Quick Facts
Time
10 minutes
Difficulty
Easy
Tools
2 tools
Cost to DIY
$15-30
The TPS tells the ECU how far the throttle is open. A worn or dirty potentiometer-style TPS produces "dead spots" - the voltage briefly flatlines or jumps as you sweep it. The ECU sees this as a panic move and dumps fuel or shifts oddly. Drive-by-wire systems use two TPS sensors that must agree within 5%.
🛠 What You'll Need
- Digital multimeter (DC volts) (shop a digital multimeter on Amazon)
- OBD2 scanner with TPS live data (shop a Bluetooth OBD2 scanner on Amazon)
- Back-probe pins (shop back-probe pin set on Amazon)
Product links above are Amazon affiliate links. AmpAuto earns a small commission at no extra cost to you.
⚠ When NOT to DIY thisOn drive-by-wire systems, never crank the throttle by hand while the engine is running - the ECU will throw a fault and may enter limp mode. Use a scan tool for any live tests with the engine on.
🎯 Expected Readings (Pass/Fail Reference)
| Closed throttle voltage | 0.4 - 0.9 V DC |
| Wide-open throttle voltage | 4.0 - 4.7 V DC |
| Voltage sweep | Smooth, linear, NO flat spots or jumps |
| TPS supply voltage (reference) | 5.0 V (within 0.1 V) at the TPS connector |
| Drive-by-wire: TPS1 vs TPS2 at any throttle position | Within 5% of each other |
Numbers are typical. Always cross-check against your factory service manual for the exact spec.
📝 Step-by-Step Test Procedure
- Pull codesP0120 (circuit), P0121 (range/performance), P0122 (low input), P0123 (high input), P0124 (intermittent). Drive-by-wire also has P2135 (TPS1/TPS2 voltage correlation).
- Identify cable vs drive-by-wireIf the throttle body has a visible cable from the gas pedal: cable. If there is only an electrical connector on the throttle body: drive-by-wire (electronic).
- Locate the TPSCable throttle: a small box on the side of the throttle body, 3 wires (5V ref, ground, signal). Drive-by-wire: built into the throttle body itself; usually 6 wires (two TPS signals plus motor).
- Check the 5V reference (key on, engine off)Back-probe the reference wire. Multimeter on DC volts. Should read 5.0 V (±0.1). If lower, the wiring or ECU 5V supply is bad - not the TPS.
- Voltage sweep testBack-probe the signal wire. Key on, engine off. With the throttle closed, voltage should read 0.4-0.9 V. SLOWLY open the throttle by hand (cable type only - or use scan tool for drive-by-wire). Voltage should rise smoothly to 4.0-4.7 V at wide open. Any flat spot or sudden jump = bad TPS.
- Scan tool live data checkFor drive-by-wire: watch TPS% in scan tool while a helper slowly pushes the pedal. Should sweep smoothly 0% to 100%. Look for dead bands or correlation errors between TPS1 and TPS2.
- Closed-throttle relearnAfter installing a new TPS or cleaning the throttle body, most cars need a relearn: key on for 30 seconds without starting, then start and idle 60 seconds. Drive-by-wire may need a scan tool relearn.
- Inspect throttle body and replace TPS if neededCarbon at the throttle plate edges causes false high-TPS-at-idle readings. Clean before condemning the TPS. shop throttle position sensors on Amazon.
✅ Pass / Fail Criteria
✅ PASS
0.5V closed, 4.5V open, smooth linear sweep, 5.0V supply, TPS1/TPS2 within 5% (drive-by-wire)
❌ FAIL
Voltage outside 0.4-4.7V range, dead spots or jumps in sweep, low 5V supply, TPS1/TPS2 mismatch over 5%
🔧 If It Fails - What To Do Next
Cable-style TPS: replace ($15-40 part). Drive-by-wire: usually replace the entire throttle body assembly ($150-400). Clean throttle plates first - carbon often mimics TPS failure. See How to clean a throttle body and What is a throttle body?
🔗 Related Guides
❓ Frequently Asked Questions
What does a bad TPS feel like?
Hesitation on tip-in, surging at steady cruise, erratic shifts on automatics, or a stuck-high idle.
Can I drive with a bad TPS?
Yes, in limp mode. Some cars will refuse to go above 2,000 RPM until you replace it. Replace soon.
What is the difference between TPS and APP (accelerator pedal position)?
TPS is on the throttle body; APP is on the gas pedal. Drive-by-wire systems use both - ECU compares them.
How long does a TPS last?
100,000+ miles for the sensor itself; the contacts inside wear out from constant sweeping.
Do I need to relearn after replacing a TPS?
Usually yes. Key-on/off cycles or a scan tool relearn restores idle and pedal mapping.
Will a dirty throttle body cause TPS codes?
Sometimes - carbon at the plate edges can hold the throttle slightly open, throwing P0121.