What it means
Catalyst temperature sensor at bank 1 sensor 2 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 2 catalyst temperature sensor measures exhaust temperature at the downstream sensor position on bank 1. P042C sets when the control module sees a signal below its expected range, often because the signal wire is shorted to ground, making the reading unusable.
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
- Record freeze-frame data and check whether the bank 1 sensor 2 PID is pinned low or implausible compared with other temperature readings.
- Inspect the downstream sensor connector for water, corrosion, loose terminals, or a pin pushed back into the housing.
- Trace its harness near the exhaust and brackets for insulation rubbed through or wires trapped against metal.
- With the fault active, gently move accessible harness sections while watching the PID for a change that points to an intermittent short.
- Test the signal circuit for a short to ground and check sensor and wiring continuity against the manufacturer's specification.
Common fixes
- Dry and reconnect the bank 1 sensor 2 connector and secure any loose terminal.
- Repair chafed wiring shorting the signal to ground.
- Replace a corroded connector or damaged harness section.
- Replace the bank 1 sensor 2 temperature sensor if it fails the manufacturer's electrical checks.
Can I keep driving?
If the engine runs normally, limited driving is usually possible, but avoid hard acceleration if sulfur odor or performance problems appear. Emissions monitoring may be affected and an inspection may be failed.
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.