P0123 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.
DTC/P0123·Honda
P0123 on Honda: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeverityNot safe to driveHonda
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.
What does P0123 mean on a Honda?
Honda Civic
2006-20158th/9th gen R18 engines occasionally log P0123 after aftermarket intake installs that disturb the throttle body connector. Honda's idle relearn (throttle body cleaned, KOEO 10 min with A/C off) is required after any TPS work.
What causes P0123 on a Honda?
Beyond the generic causes listed on the main P0123 page, these are the Honda-specific patterns we see most often:
Honda CivicDisturbed throttle body connector after intake or air box mods
Honda CivicMissed idle relearn after battery disconnect or throttle body service
How to diagnose P0123 on a Honda with OBD2
Follow these steps to pinpoint the root cause of P0123:
- 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 on a Honda (Honda parts and labour typically run 15% below the average for this code).
Prices estimated as of May 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0123 on Honda
These codes commonly cluster with P0123 on Honda vehicles:
FAQ: P0123 on Honda
Will P0123 clear itself if I just drive it?
No. It's a hard electrical fault. The MIL might go out after several drive cycles without the fault recurring, but the underlying wiring or sensor issue almost always comes back within minutes.
Will P0123 make my car fail an emissions inspection?
Yes. It's a stored powertrain code with the MIL on, which is an automatic fail at any OBD2 inspection.
Do I need a new throttle body or just the sensor?
On older cable-throttle cars (mostly pre-2005) the TPS is a bolt-on €40-80 part. On drive-by-wire systems the sensor is integrated into the throttle body and you replace the whole assembly.
Why did my car go into limp mode with this code?
The PCM can't trust the throttle signal, so it ignores the pedal and holds the throttle at a fixed low opening (usually 1200-1500 RPM) to prevent unintended acceleration.
Do I need to relearn the throttle after replacing it?
Yes, on nearly all drive-by-wire cars. Most brands need a specific idle/throttle relearn procedure (Toyota, Honda, VW, BMW all have their own). Skipping this leaves rough idle even after a good part is fitted.
Looking for the full P0123 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0123 guideSkanyx · Honda
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