What Does P1174 Mean?
This code indicates the adaptive fuel trim (additive correction) for bank 1 has reached its malfunction threshold. Additive fuel trim operates at idle and low-load conditions, adding or subtracting a fixed amount of fuel. When this correction reaches its maximum limit, the PCM sets this code because it can no longer adequately compensate for the deviation from stoichiometric. This typically points to a metering issue affecting bank 1 at low engine speeds.
Common Causes
30%
Vacuum leak on bank 1 intake manifold gasket or associated vacuum hoses
25%
Leaking or clogged fuel injector(s) on bank 1
20%
Faulty mass airflow (MAF) sensor under-reporting or over-reporting airflow
15%
Degraded upstream oxygen sensor on bank 1 providing inaccurate feedback
10%
Crankcase ventilation (PCV) system fault introducing unmeasured air
Diagnostic Steps
1
Record bank 1 additive and multiplicative fuel trim values at idle; additive values beyond +/-10% at idle indicate the correction is nearing its limit.
2
Perform a smoke test on the intake manifold and all vacuum connections on bank 1 to identify any vacuum leaks.
3
Check the PCV valve and hose for proper operation; a stuck-open PCV introduces unmeasured air that causes lean additive trim correction.
4
Test fuel injector flow rates on bank 1 using a flow bench or noid light test; uneven spray patterns or flow rates indicate clogged or leaking injectors.
5
Clean or replace the MAF sensor and verify its readings match manufacturer specifications at idle airflow.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
This code indicates the adaptive fuel trim (additive correction) for bank 1 has reached its malfunction threshold. Additive fuel trim operates at idle and low-load conditions, adding or subtracting a fixed amount of fuel. When this correction reaches its maximum limit, the PCM sets this code because...
The most common cause of P1174 (Fuel Trim Adaptation Additve Bank 1 Malfunction) is: Vacuum leak on bank 1 intake manifold gasket or associated vacuum hoses
Typical repair costs for P1174 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
No immediate safety concern, but the engine may idle rough and fuel economy will suffer. If the lean condition is severe, engine misfires at idle could cause rough running or stalling in traffic.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1174 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel / Air Metering
Difficulty
Type
Manufacturer
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