Failed or contaminated downstream heated oxygen sensor (HO2S12) on bank 1; Exhaust leak between the catalyst and the downstream sensor, drawing in air and skewing the reading lean; Wiring damage or corroded connector pins in the HO2S12 circuit, including chafed harness near the exhaust; Aging or degraded catalytic converter on bank 1 that no longer stores oxygen properly; Vacuum leak or unmetered air entering upstream of the sensor, causing a genuine lean condition the sensor correctly reports; Low fuel pressure or a weak fuel pump delivering insufficient volume under load; Engine coolant temperature sensor bias causing the module to fuel incorrectly during warm-up

DTC codes / Jaguar codes / P1137

P1137 · JaguarLack Of HO2S12 Switches Sensor Indicates Lean

Q: What does code P1137 mean?

Lack Of HO2S12 Switches Sensor Indicates Lean. P1137 on a Jaguar means the engine control module has monitored the downstream heated oxygen sensor on bank 1 (HO2S12) and found its voltage signal stuck lean, indicating the sensor is not switching rich-to-lean as expected. The computer expects the post-catalyst sensor to oscillate within a calibrated range once the catalyst is lit, and this code sets when the signal remains below the lean threshold for too long.

P1137 on a Jaguar means the engine control module has monitored the downstream heated oxygen sensor on bank 1 (HO2S12) and found its voltage signal stuck lean, indicating the sensor is not switching rich-to-lean as expected. The computer expects the post-catalyst sensor to oscillate within a calibrated range once the catalyst is lit, and this code sets when the signal remains below the lean threshold for too long.

SystemPowertrain

Code typeJaguar specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other symptoms besides the warning light
Slightly rough idle or hesitation on light acceleration in some cases
A faint sulfur or rotten-egg smell from the exhaust if the catalyst is being overfuelled
Reduced fuel economy noticed over several tanks of fuel
Intermittent misfire or stumble when the engine is cold
Failed emissions test with elevated hydrocarbon or carbon monoxide readings

Common causes, most likely first

Failed or contaminated downstream heated oxygen sensor (HO2S12) on bank 1
Exhaust leak between the catalyst and the downstream sensor, drawing in air and skewing the reading lean
Wiring damage or corroded connector pins in the HO2S12 circuit, including chafed harness near the exhaust
Aging or degraded catalytic converter on bank 1 that no longer stores oxygen properly
Vacuum leak or unmetered air entering upstream of the sensor, causing a genuine lean condition the sensor correctly reports
Low fuel pressure or a weak fuel pump delivering insufficient volume under load
Engine coolant temperature sensor bias causing the module to fuel incorrectly during warm-up

How to diagnose and fix it

Scan all modules for stored and pending codes, then record freeze-frame data for P1137 to see the conditions at fault set
Inspect the HO2S12 harness and connector for chafing, corrosion, or oil contamination, and check the sensor ground circuit
Smoke-test the exhaust system from the catalyst back to the sensor to rule out an air leak before condemning the sensor
Graph the HO2S12 voltage on a scan tool while holding a steady cruise; a healthy sensor should switch rich-to-lean several times per second
Check fuel pressure and fuel trim data to confirm whether the lean reading is real or a sensor reporting error
If the sensor is slow or stuck lean with no exhaust leak, replace the downstream heated oxygen sensor and clear the code
After repair, verify the catalyst monitor runs to completion and confirm HO2S12 switching returns to normal

Exhaust leaks mimic a dead oxygen sensor

A small crack or failed gasket between the catalyst and the downstream sensor pulls outside air into the exhaust stream, and the sensor faithfully reports lean, so technicians replace a healthy sensor and the code returns within a few drive cycles.
Jaguar's downstream sensor on bank 1 is often contaminated by coolant or oil seeping past a failing gasket, which coats the sensing element and slows its switching without setting a heater circuit code.
P1137 does not always mean the catalytic converter has failed; a lazy upstream sensor or a biased coolant temperature sensor can push fuel trims lean enough to keep the downstream sensor below its switching threshold.
On supercharged and turbocharged Jaguar engines, a boost leak after the throttle body can produce a genuine lean condition that the downstream sensor detects before the upstream sensor sets its own code.
Clearing P1137 without repairing the cause will usually result in the code returning after two or three complete drive cycles once the monitor re-runs, so always confirm the repair with live data.

Can I keep driving with P1137?

You can usually drive the car short distances to a workshop, but avoid sustained high-speed or heavy-load driving because a genuine lean condition can raise exhaust temperatures and damage the catalyst. If the check engine light starts flashing or you feel a misfire, stop driving and have the car towed.

Tools that help

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Guidance is general and written for Jaguar vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.