P0051 on 2003-2009 Toyota 4Runner — HO2S Heater Control Circuit Low (Bank 2 Sensor 1)
1 vehicles · 1 makes
How to diagnose and fix P0051: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Toyota 4Runner · 2003–2009
Owners of fourth-generation 4Runners report code P0031, a heater circuit fault for the bank 1 upstream sensor, often together with P0051 for bank 2, with the check engine and VSC lights on. In one 2003 V6 case, replacing both sensors and the engine computer did not clear the codes; the cause was a broken wire through the firewall to the A/F heater relay. Applies to: 2003-2009 Toyota 4Runner with the 4.0L 1GR-FE V6 or the 4.7L 2UZ-FE V8. The owner reports linked here are from a 2003 V6 and 2004, 2005 and 2007 V8 trucks. The V6 uses air-fuel ratio sensors in this position; owners say early (pre-2005) V8s use conventional oxygen sensors there. Mileage when it happened, as stated in the linked owner reports: 36,000 miles on a 2007.
Common Symptoms
- Check engine light on with code P0031
- VSC TRAC and VSC OFF lights come on with the engine light
- Check engine light comes straight back after codes are cleared
How to Fix
Have the codes diagnosed before buying parts: a technician should check the sensor heaters, the A/F heater relay, and the wiring and connectors. One owner who fitted the wrong type of replacement sensor got both codes right after installation.
Sources for this issue (5)
- Toyota 4Runner Forum: O2 Sensor Replace - p0031 Code?forum
- Toyota 4Runner Forum: P0031 oxygen sensor locationforum
- Toyota 4Runner Forum: Simultaneous P0031 and P0051 Codesforum
- The Track Ahead: P0031 and P0051 Codes - Check Engine Light, VSC TRAC, VSC OFF Light (owner project blog)forum
- Toyota 4Runner Forum: Swapped out O2 sensors and getting P0031 and P0051forum
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P0051 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0051 mean?
P0051 stands for "HO2S Heater Control Circuit Low (Bank 2 Sensor 1)." The PCM detects low voltage (short to ground or open) in the heater control circuit of the upstream O2 sensor on Bank 2, Sensor 1.
What are the most common causes of P0051?
The most common causes of P0051 are: Open/short to ground in heater wiring, Failed O2 sensor heater, Corroded connector, Blown fuse. The specific cause varies by vehicle.
How much does it cost to fix P0051?
Repair costs vary widely depending on the root cause and vehicle.
Which vehicles are affected by P0051?
Au7o has documented P0051 across 1 vehicle models from 1 manufacturers: Toyota.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.