What it means
Catalyst temperature sensor at bank 1 sensor 1 below lower plausibility — short to ground. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The bank 1 sensor 1 catalyst temperature sensor measures exhaust temperature near the upstream side of the catalytic converter. The control module detects a signal below the expected range, commonly when the signal wire is shorted to ground, so it cannot reliably assess catalyst temperature.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
How to diagnose it
- Save freeze-frame data and check the bank 1 sensor 1 temperature PID for a reading pinned low or implausible compared with a cold engine and other temperature data.
- Inspect the sensor connector for water, corrosion, loose terminals, or a pin pushed back into the housing.
- Follow the bank 1 sensor 1 harness and look for insulation rubbed through against the exhaust, brackets, or body.
- With the fault present, gently move accessible sections of the harness while watching the sensor PID to identify an intermittent short.
- Check the signal circuit for a short to ground and verify sensor and wiring continuity against the manufacturer's specification before replacing parts.
Common fixes
- Dry and reconnect the bank 1 sensor 1 connector; correct a loose or pushed-back terminal.
- Repair chafed insulation or wiring that is shorting the signal to ground.
- Replace a corroded connector or damaged harness section.
- Replace the sensor if it fails the manufacturer's electrical checks after wiring repairs.
Can I keep driving?
If the engine runs normally, limited driving is generally possible, but avoid hard acceleration if you notice sulfur odor or declining performance. The fault can interfere with emissions control checks and cause an inspection failure.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.