What Does P1125 Mean?
P1125 indicates the long-term fuel trim for Bank 2 in the additive air system is showing a system-too-rich condition. The ECM has been subtracting fuel over an extended period to compensate for excessive richness on Bank 2. This suggests there is either too much fuel being delivered or too little air reaching the combustion chambers on that bank. Prolonged rich operation leads to catalytic converter damage, fouled spark plugs, and increased emissions.
Common Causes
28%
Leaking fuel injector(s) on Bank 2 delivering excess fuel
25%
Faulty Bank 2 O2 sensor reporting false lean, causing ECM to over-fuel
18%
Restricted air intake or clogged air filter reducing airflow to Bank 2
17%
Fuel pressure regulator stuck or leaking, causing high system fuel pressure
12%
EVAP purge valve stuck open, allowing excess fuel vapors into intake
Diagnostic Steps
1
Step 1: Check long-term fuel trim (LTFT) for Bank 2. Significant negative values (e.g., -15% or more) confirm the ECM is actively removing fuel to compensate for a rich condition.
2
Step 2: Compare Bank 1 and Bank 2 fuel trims. If only Bank 2 is rich, the issue is likely bank-specific (injector, intake runner, O2 sensor). If both banks are rich, suspect a system-wide cause (fuel pressure, purge valve).
3
Step 3: Test fuel pressure with a gauge. At idle, pressure should be within manufacturer specification (typically 35–65 psi for port injection). Elevated pressure indicates a faulty regulator.
4
Step 4: Perform an injector balance test or leak-down test on Bank 2 injectors. A leaking injector will show fuel seepage even when not commanded on.
5
Step 5: Monitor Bank 2 Sensor 1 O2 readings. A sensor stuck lean (below 0.2V) would cause the ECM to add fuel continuously. Replace if the sensor is not switching properly.
Estimated Repair Cost
$75 - $500
Parts + labor, varies by vehicle and location
P1125 indicates the long-term fuel trim for Bank 2 in the additive air system is showing a system-too-rich condition. The ECM has been subtracting fuel over an extended period to compensate for excessive richness on Bank 2. This suggests there is either too much fuel being delivered or too little ai...
The most common cause of P1125 (Long Term Fuel Trim Add.Air.,Bank2 System too Rich) is: Leaking fuel injector(s) on Bank 2 delivering excess fuel
Typical repair costs for P1125 range from $75 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Rich running conditions can overheat catalytic converters, potentially causing a fire if the converter reaches extreme temperatures. Black smoke from the exhaust may also impair visibility for following vehicles.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1125 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel Delivery / Emissions Control
Difficulty
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