What Does P1165 Mean?
This code indicates that the long-term fuel trim (LTFT) for bank 1 at idle and low-load conditions (range 1) has exceeded its maximum rich correction limit. The PCM is trying to subtract fuel beyond its calibrated threshold because the engine is running too rich. This means the adaptive fuel system has exhausted its ability to compensate for an over-fueling condition on bank 1 at idle/low RPM operating ranges.
Common Causes
30%
Leaking fuel injector(s) on bank 1 causing excess fuel delivery at idle
25%
Excessive fuel pressure from a faulty fuel pressure regulator
20%
Faulty upstream oxygen sensor on bank 1 incorrectly reporting lean
15%
EVAP system purge valve stuck open, flooding the intake with fuel vapor
10%
Contaminated MAF sensor reading lower than actual airflow, causing PCM to under-calculate air
Diagnostic Steps
1
Record bank 1 short-term and long-term fuel trims at idle; LTFT values of -20% or more negative confirm the rich limit condition.
2
Check fuel pressure at idle with a mechanical gauge; compare to specification. Elevated pressure indicates a faulty regulator or restricted return line.
3
Perform an injector leak-down test by priming fuel pressure and monitoring pressure drop over several minutes with the engine off; excessive drop indicates a leaking injector.
4
Disconnect the EVAP purge line at the intake manifold and plug it; if fuel trims immediately improve, the purge valve is stuck open.
5
Clean or replace the MAF sensor if contaminated; verify airflow readings match known-good values at idle.
Estimated Repair Cost
$150 - $600
Parts + labor, varies by vehicle and location
This code indicates that the long-term fuel trim (LTFT) for bank 1 at idle and low-load conditions (range 1) has exceeded its maximum rich correction limit. The PCM is trying to subtract fuel beyond its calibrated threshold because the engine is running too rich. This means the adaptive fuel system ...
The most common cause of P1165 (Bank1, Long Term Fuel Trim, Range 1 Rich Limit Exceeded) is: Leaking fuel injector(s) on bank 1 causing excess fuel delivery at idle
Typical repair costs for P1165 range from $150 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A persistent rich condition increases carbon monoxide emissions and can cause catalytic converter overheating. In severe cases, raw fuel in the exhaust can pose a fire risk at the converter.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1165 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel / Air Metering
Difficulty
Type
Manufacturer
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