Leaking or stuck-open fuel injectors on one or both banks, delivering excess fuel into the cylinders.; A faulty mass air flow sensor that under-reports airflow, causing the engine control module to calculate a rich mixture.; A failing engine coolant temperature sensor that stays cold, making the engine control module add extra fuel for cold-start enrichment.; A leaking fuel pressure regulator or a restricted fuel return line, raising fuel pressure beyond specification.; A faulty oxygen sensor that falsely reports a lean condition, prompting the engine control module to richen the mixture.; Evaporative emissions system purge valve stuck open, allowing fuel vapor to be drawn into the intake continuously.; Mechanical issues such as low compression or a jumped timing chain that alter the air-fuel mixture on both banks.

DTC codes / Jaguar codes / P1172

P1172 · JaguarSystem Too Rich Banks 1 And 2 (Rich Fuel Fault)

Q: What does code P1172 mean?

System Too Rich Banks 1 And 2 (Rich Fuel Fault). P1172 on a Jaguar indicates that the engine control module has detected a rich fuel condition on both banks of the engine, meaning the air-fuel mixture contains too much fuel and not enough air. The computer monitors the oxygen sensors and fuel trim values, and when the long-term fuel trim on both banks exceeds the rich threshold, it stores this code and illuminates the check engine light.

P1172 on a Jaguar indicates that the engine control module has detected a rich fuel condition on both banks of the engine, meaning the air-fuel mixture contains too much fuel and not enough air. The computer monitors the oxygen sensors and fuel trim values, and when the long-term fuel trim on both banks exceeds the rich threshold, it stores this code and illuminates the check engine light.

SystemPowertrain

Code typeJaguar specific

SeverityMedium

Fix difficultyProfessional

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms.
A strong gasoline odor from the exhaust, especially at idle or after a cold start.
Black, sooty exhaust smoke or black deposits on the rear bumper above the tailpipe.
Reduced fuel economy, with more frequent trips to the fuel station.
Rough idle, hesitation, or stumbling during acceleration due to excessive fuel.
Possible misfire codes or catalytic converter efficiency codes stored alongside P1172.

Common causes, most likely first

Leaking or stuck-open fuel injectors on one or both banks, delivering excess fuel into the cylinders.
A faulty mass air flow sensor that under-reports airflow, causing the engine control module to calculate a rich mixture.
A failing engine coolant temperature sensor that stays cold, making the engine control module add extra fuel for cold-start enrichment.
A leaking fuel pressure regulator or a restricted fuel return line, raising fuel pressure beyond specification.
A faulty oxygen sensor that falsely reports a lean condition, prompting the engine control module to richen the mixture.
Evaporative emissions system purge valve stuck open, allowing fuel vapor to be drawn into the intake continuously.
Mechanical issues such as low compression or a jumped timing chain that alter the air-fuel mixture on both banks.

How to diagnose and fix it

Connect a scan tool and record freeze-frame data and long-term fuel trim values on both banks to confirm the rich condition.
Inspect the air intake system for restrictions or leaks after the mass air flow sensor, and clean or replace the sensor if contaminated.
Check fuel pressure with a gauge and compare to Jaguar specifications; replace the fuel pressure regulator if pressure is too high.
Perform an injector balance test or remove injectors for bench testing to identify leaking or stuck-open injectors.
Test the engine coolant temperature sensor resistance against a temperature chart and replace if out of range.
Check the evaporative emissions purge valve for sticking open by commanding it closed with a scan tool and observing fuel trims.
Inspect oxygen sensor operation with a graphing scan tool and replace any sensor that responds sluggishly or incorrectly.

Rich condition traps on Jaguar V8 engines

A common oversight is assuming both banks are rich due to separate injector failures, when a single faulty mass air flow sensor or fuel pressure regulator affects both banks simultaneously.
Jaguar V8 engines are known for timing chain tensioner failures that can cause a jumped timing chain, leading to rich fuel trims on both banks without any misfire codes.
A stuck-open purge valve on the evaporative emissions system can cause a rich condition at idle that disappears at higher engine speeds, mimicking a fuel injector problem.
Oxygen sensor signal wires routed too close to spark plug wires can pick up electrical interference and report a false lean condition, causing the engine control module to richen the mixture.
Before replacing expensive components, verify that the engine oil does not smell of fuel, as repeated rich operation can dilute the oil and cause further engine wear.

Can I keep driving with P1172?

You can drive the vehicle short distances to a repair shop, but avoid prolonged driving because the rich mixture can quickly overheat and damage the catalytic converters. Do not tow heavy loads or drive at high speeds until the fault is repaired.

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.