OBD-II trouble code
P2235: O2 Sensor Signal Circuit Shorted to Heater Circuit (Bank 2, Sensor 2)
A post-converter sensor on the second bank, where the repair is usually simple and the repeat is usually self-inflicted: on a four-sensor vehicle the two downstream sensors are different part numbers, and fitting the wrong one leaves a lead that will short again.
Quick facts
- System
- Powertrain
- Category
- Oxygen Sensor
- Severity
- Low severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $650
- DIY difficulty
- Intermediate DIY
What does P2235 mean?
This sensor sits behind the catalytic converter on the bank that does not contain cylinder 1. It plays no part in deciding how much fuel the engine gets. Its job is to look at what comes out of the converter and let the module judge whether that converter is still doing useful work. So the driving consequences of this code are close to nothing — the engine runs the same, the economy is the same — and what you actually lose is the ability to complete an emissions readiness monitor and pass an inspection.
The mechanism is common to the whole family. One cable carries a heater on battery voltage and a signal element that cannot exceed about a volt, and when the insulation between them fails, the module reads a signal far above anything an oxygen sensor can produce. It stores the code without needing to interpret anything.
The part of this that is worth reading before ordering anything is what happens after the repair, because this is the position in the family where the fix most often creates the next fault. A V-configuration or flat engine with four oxygen sensors has two downstream sensors, and they look interchangeable in a catalogue listing that only says "downstream oxygen sensor". They frequently are not. The two banks sit different distances from the module and the connector, and manufacturers accommodate that with different pigtail lengths, different connector keying, and sometimes different routing clips moulded into the lead. Fit the shorter bank 1 downstream sensor to bank 2 and it will physically connect, the engine will run, and the code will clear — and the lead will now be pulled taut across a run it was never cut for. A taut lead has no slack to absorb engine movement, sits closer to whatever it passes, and finds the exhaust or a bracket edge within a few thousand miles. That is a second short in the same circuit, and it is very easy to blame on a defective part rather than on the part number.
So the rule for this position is simple: order by the specific position, not by the description, and when the new sensor is in, route the lead through the original clips with the original slack before the connector goes home. If a clip is missing because a previous repair left it out, replace it. The cost of doing that is a few minutes. The cost of not doing it is the whole job again.
There is a second point specific to a two-bank vehicle. The catalyst monitor runs per bank, but readiness is reported for the vehicle as a whole. One corrupted downstream sensor is enough to hold the entire readiness set incomplete, so an inspection failure here does not mean three of the four sensors are also bad — it means one is, and it is enough. That is worth knowing when a shop's quote arrives with more than one sensor on it.
Finally, the same warning that applies to any downstream sensor fault applies with force. If a converter efficiency code for this bank is stored alongside this one, it was reached using a voltage that came from the heater circuit. That verdict is not evidence. Repair the short, clear everything, drive the vehicle until the monitor runs again, and only then let anyone price exhaust parts.
Common causes
- Wrong downstream sensor fitted for the position, leaving the lead short and under tension against a hot or sharp surface
- Lead routed outside its original clips after a previous repair, allowing it to contact the exhaust or a bracket
- Water and road salt entering the connector and bridging the heater and signal cavities
- Abrasion through the jacket at an underbody clip, heat shield edge or hanger
- Internal short inside the sensor between the heater element and the signal terminals
- Stone or debris impact on the under-vehicle section of the lead
- Corrosion wicking along the cable from a previously damaged section
- Damage during exhaust, converter or heat shield work on that bank
Symptoms
- Check engine light with no change in how the vehicle drives
- A downstream sensor voltage held above one volt and not moving
- Emissions readiness monitors that will not complete, so the vehicle cannot be presented for inspection
- Emissions test failure on readiness rather than on measured output
- A bank 2 catalyst efficiency code stored alongside, which is a consequence of this fault rather than proof of a bad converter
- The fault reappearing a few thousand miles after a sensor was replaced, which points at part number or routing rather than at the sensor
- Blown oxygen sensor heater fuse on applications where sensors share a supply
- Normal fuel economy and normal power
Diagnostic steps
- 1.Confirm which physical sensor the scan tool means. On a four-sensor vehicle it is easy to end up at the wrong downstream unit, and the two are not always in mirrored positions.
- 2.Read the live voltage. A value pinned above one volt is beyond anything an oxygen sensor can generate and confirms heater voltage on the signal line.
- 3.Unplug the sensor and check the vehicle-side signal wire with the key on. Battery-level voltage there places the fault in the harness rather than the sensor.
- 4.With the sensor unplugged, measure resistance between its heater terminals and its signal terminal. Continuity between the two condemns the sensor.
- 5.Ask whether this sensor has been replaced before, and if so compare the fitted lead length and connector against the correct part for this exact position.
- 6.Trace the lead from the sensor to the connector and note every clip it should pass through. A lead that is taut, or that bypasses a clip, has found its own route to the next short.
- 7.Inspect the connector for water, salt and corrosion between the heater and signal cavities.
- 8.Check the oxygen sensor heater fuse, since a shared supply can take several sensors offline from one short.
- 9.After repair, clear all codes, complete a full drive cycle and let the catalyst monitor run before any converter decision is made.
Repair cost
$100 – $650
Diagnosis is $90 to $180. A correct downstream sensor for this position is $50 to $250 in parts and $120 to $420 fitted; the labour is usually modest because the sensor is accessible from underneath, but rusted threads on an older vehicle can turn a twenty-minute job into a two-hour one. A harness or connector repair runs $110 to $350. Buying by position rather than by description is worth doing even when the correct part costs more, because the repeat failure it prevents costs the whole job again. As always in this family, the expense this page is written to avoid is a $500 to $2,500 converter replaced on the word of a sensor that was reporting heater voltage.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with oxygen sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.