Leaking or sticking fuel injectors delivering too much fuel; Faulty mass air flow sensor over-reporting air intake, causing excess fuel delivery; High fuel pressure from a failed fuel pressure regulator or restricted return line; Leaking evaporative emissions purge valve allowing fuel vapor into the intake; Contaminated engine oil with fuel dilution affecting crankcase ventilation; Worn or incorrectly gapped spark plugs causing incomplete combustion; Faulty oxygen sensors biased rich, misleading the fuel trim strategy

DTC codes / Jaguar codes / P1179

P1179 · JaguarLong Term Fuel Trim Too Rich Banks 1 And 2 (AMFR)

Q: What does code P1179 mean?

Long Term Fuel Trim Too Rich Banks 1 And 2 (AMFR). P1179 on Jaguar vehicles means the engine control module has detected that the long-term fuel trim on both banks has reached its rich limit, indicating the engine is running too rich and the computer can no longer lean it out. The adaptive fuel control has maxed out its negative correction, typically beyond -20 to -25 percent, which signals excess fuel or a measurement error.

P1179 on Jaguar vehicles means the engine control module has detected that the long-term fuel trim on both banks has reached its rich limit, indicating the engine is running too rich and the computer can no longer lean it out. The adaptive fuel control has maxed out its negative correction, typically beyond -20 to -25 percent, which signals excess fuel or a measurement error.

SystemPowertrain

Code typeJaguar specific

SeverityMedium

Fix difficultyProfessional

AreaFuel and air metering

Symptoms you may notice

Often no symptoms besides the warning light, especially in early stages
Noticeable drop in fuel economy and a strong fuel smell from the exhaust
Black sooty smoke from the tailpipe under acceleration
Rough idle or engine stumbling due to overly rich mixture
Failed emissions test with high carbon monoxide readings
Spark plugs fouling prematurely with black deposits

Common causes, most likely first

Leaking or sticking fuel injectors delivering too much fuel
Faulty mass air flow sensor over-reporting air intake, causing excess fuel delivery
High fuel pressure from a failed fuel pressure regulator or restricted return line
Leaking evaporative emissions purge valve allowing fuel vapor into the intake
Contaminated engine oil with fuel dilution affecting crankcase ventilation
Worn or incorrectly gapped spark plugs causing incomplete combustion
Faulty oxygen sensors biased rich, misleading the fuel trim strategy

How to diagnose and fix it

Connect a scan tool and record long-term fuel trim values on both banks to confirm the rich condition
Inspect spark plugs for black soot and replace if fouled, checking gap and heat range
Test fuel pressure with a gauge and compare to Jaguar specifications; replace regulator if high
Perform an injector balance test or remove injectors for professional cleaning and flow testing
Check the evaporative purge valve for sticking open by commanding it closed and monitoring fuel trim
Clean or replace the mass air flow sensor after verifying its live readings against expected values
Recheck fuel trim after repairs and clear the code, then road test to confirm the fix

Rich fuel trim traps on Jaguar V8 engines

A stuck-open purge valve is a frequent culprit that mimics injector problems and is often overlooked because it does not always set an EVAP code.
Fuel dilution in the oil from repeated short trips can skew crankcase ventilation and cause rich trims without any faulty fuel system component.
Aftermarket air filters that are over-oiled can contaminate the mass air flow sensor and cause it to over-report airflow, leading to rich fuel trim.
The long-term fuel trim limit on many Jaguars is around -25 percent, so a reading near that value confirms the code but does not pinpoint the cause.
Replacing oxygen sensors blindly is a common misdiagnosis; the sensors are usually reporting correctly when both banks are rich.

Can I keep driving with P1179?

You can drive the car short distances to a repair shop, but avoid sustained high-speed driving or heavy loads because the rich mixture can overheat and damage the catalytic converters. Prolonged driving with P1179 will worsen fuel dilution and emissions, so schedule diagnosis promptly.

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.