What Does P1084 Mean?
The ECM has detected a rich fuel mixture condition based on feedback from the upstream oxygen sensor on Bank 1. The air-fuel ratio is consistently richer than optimal, indicating too much fuel or insufficient air.
Common Causes
30%
Faulty or leaking fuel injector(s) delivering excess fuel
25%
High fuel pressure due to failed pressure regulator
20%
Contaminated or faulty mass airflow sensor reading low
15%
Restricted air intake or dirty air filter
10%
Faulty oxygen sensor or coolant temperature sensor
Diagnostic Steps
1
Step 1: Inspect air filter and intake system for restrictions or blockages
2
Step 2: Test fuel pressure and compare to specifications (may be too high)
3
Step 3: Monitor fuel trim values (STFT and LTFT) - should show negative corrections
4
Step 4: Check MAF sensor reading against known-good values at idle
5
Step 5: Perform fuel injector balance test or monitor injector pulse width
Estimated Repair Cost
$150 - $900
Parts + labor, varies by vehicle and location
The ECM has detected a rich fuel mixture condition based on feedback from the upstream oxygen sensor on Bank 1. The air-fuel ratio is consistently richer than optimal, indicating too much fuel or insufficient air.
The most common cause of P1084 (Fuel Control Mixture Rich (Bank 1 Sensor 1)) is: Faulty or leaking fuel injector(s) delivering excess fuel
Typical repair costs for P1084 range from $150 to $900, depending on the vehicle, location, and whether you do it yourself or go to a shop.
May cause poor fuel economy, rough idle, and black exhaust smoke. Safe to drive but will damage catalytic converter if left unrepaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1084 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel System and Air Intake
Difficulty
Type
Manufacturer
Recommended Tools
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