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P0122 on Honda: Causes, Symptoms and Fix Cost

Quick Answer

Not safe to drive

P0122 on a Honda means the ECU is seeing an abnormally low voltage on throttle position sensor circuit A, typically under 0.2V when it expects 0.5V to 4.5V. Most cars drop into limp mode with capped throttle.

Severity
Moderate · Electrical

Connect a standard OBD2 adapter (Bluetooth LE on iPhone) to your Honda and Skanyx tells you what P0122 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.

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What does P0122 mean on a Honda?

The Quick Answer above is the generic definition. What follows is the model-specific detail for the Honda models that log P0122.

Honda Civic

2006-2015 (R18A 1.8L, 8th and 9th gen)

Uncommon on the Civic, but when it appears the throttle body assembly is the usual culprit. After any throttle work the ECU has to relearn idle or it stays unstable: with all electrical loads off, hold about 3,000 rpm in Park or Neutral until the radiator fan comes on, then let the engine idle for about 5 minutes.

Source: ricksfreeautorepairadvice.com

Sources

  1. ricksfreeautorepairadvice.com ricksfreeautorepairadvice.com/idle-relearn-procedure-honda/

What causes P0122 on a Honda?

Beyond the generic causes listed on the main P0122 page, these are the patterns noted for Honda models:

  • Carbon buildup preventing the throttle plate from returning to true closed position

    : Honda Civic

  • Cracked solder joint on the TPS board inside the throttle body

    : Honda Civic

How to diagnose P0122 on a Honda with OBD2

  1. Read all stored codes and note companion codes such as P0222 or P2135, or other low-input codes such as P0107 that point to a shared 5V reference
  2. Watch live data for TPS1 voltage with key on, engine off. Below 0.2V confirms the low input
  3. Wiggle the throttle body connector and harness while watching live data to catch intermittent faults
  4. Backprobe the TPS signal, 5V reference, and ground pins with a multimeter. Reference should read 4.9 to 5.1V
  5. If reference and ground are good but signal stays near 0V, replace the TPS or throttle body
  6. If the 5V reference is missing, check the wiring back to the ECU for a short to ground
  7. After repair, clear codes and run the throttle body relearn per the manufacturer procedure (on some makes this needs manufacturer-level software)
  8. Road test and confirm TPS voltage sweeps smoothly from ~0.5V at closed throttle to ~4.5V at WOT

How much does P0122 cost to fix on a Honda? (EUR)

Estimated repair costs for P0122 in EUR, compiled across makes. Honda parts and labour usually land towards the lower end of each range.

Repair Parts Cost Labor Cost Total Estimate DIY Difficulty
Clean and reseat throttle body connector €0–€10 €0–€40 €0–€50 Easy
Replace standalone throttle position sensor €30–€120 €40–€90 €70–€210 Easy
Replace electronic throttle body assembly €180–€550 €80–€180 €260–€730 Moderate
Repair damaged wiring or connector pins €10–€40 €60–€180 €70–€220 Moderate
ECU diagnosis and replacement (worst case) €400–€1200 €100–€250 €500–€1450 Professional

Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.

These codes are often seen alongside P0122 or point to related issues, on any make:

Looking for the full P0122 reference (all makes, full diagnosis flow, complete repair cost matrix)? See the main P0122 guide

Diagnose P0122 on your Honda

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