P0123 on Honda: Causes, Symptoms and Fix Cost
Quick Answer
Not safe to drive
P0123 on a Honda means the ECU sees TPS 'A' signal voltage above the upper threshold (typically 4.8V of the 5V reference). The computer ignores the throttle input and falls back to limp mode.
- Severity
- Moderate · Electrical
Connect a standard OBD2 adapter (Bluetooth LE on iPhone) to your Honda and Skanyx tells you what P0123 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
Get Skanyx freeWhat does P0123 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 P0123.
Honda Civic
2006-2015
8th/9th gen R18 engines occasionally log P0123 after aftermarket intake installs that disturb the throttle body connector. After any TPS or throttle body work, run Honda's idle learn: 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
- ricksfreeautorepairadvice.com ricksfreeautorepairadvice.com/idle-relearn-procedure-honda/
What causes P0123 on a Honda?
Beyond the generic causes listed on the main P0123 page, these are the patterns noted for Honda models:
Disturbed throttle body connector after intake or air box mods
: Honda Civic
Missed idle relearn after battery disconnect or throttle body service
: Honda Civic
How to diagnose P0123 on a Honda with OBD2
- Scan for all stored codes and freeze frame. Note if P0122, P0222 or P2135 are set alongside - that changes the diagnostic path
- Key on, engine off: watch TPS1 voltage on the scan tool. Above ~4.8V at closed throttle confirms the fault
- Inspect the TPS connector for bent pins, green corrosion, or water intrusion
- Backprobe the 5V reference at the TPS - should read 4.9-5.1V. If it reads battery voltage, the reference is shorted
- Check sensor ground continuity to battery negative (should be under 0.1Ω, voltage drop under 50mV with key on)
- Unplug the TPS. Signal voltage at the ECU pin should drop to near 0V. If it stays high, the signal wire is shorted to voltage between sensor and PCM
- If wiring checks out, substitute a known-good TPS or throttle body and recheck
- Only after all above, suspect PCM 5V reference or A/D converter failure
How much does P0123 cost to fix on a Honda? (EUR)
Estimated repair costs for P0123 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 TPS connector, apply dielectric grease | €0–€15 | €0–€60 | €0–€75 | Easy |
| Replace standalone throttle position sensor (cable throttle) | €40–€180 | €40–€120 | €80–€300 | Easy |
| Replace complete electronic throttle body (drive-by-wire) | €100–€450 | €80–€220 | €180–€670 | Moderate |
| Repair TPS wiring harness (short or open circuit) | €20–€90 | €90–€260 | €110–€350 | Moderate |
| PCM replacement and reprogram | €500–€1400 | €150–€350 | €650–€1750 | Professional |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
Codes related to P0123
These codes are often seen alongside P0123 or point to related issues, on any make:
Looking for the full P0123 reference (all makes, full diagnosis flow, complete repair cost matrix)? See the main P0123 guide