Error Code P1171 is defined as Fuel System Lean During Acceleration. This refers to a problem on the front cylinder, indicating a lean condition that may be caused by leaks in either the hose or vacuum lines.

This error code is a generic code, meaning it applies to all vehicles equipped with the OBD-II system, especially vehicles made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs of course, vary from one make and/or model to another.


Injector having excessive return flow or back leakage is probably the most common of injector failure. This happens when worn parts allow excessive fuel to go through the diesel injector and return back to the fuel system or tank. As a result, rail pressure is dropped leading to hard starting or not starting at all.

Common Symptoms

Error Code P1171 triggers the Check Engine light, which is usually its most obvious symptom. Other symptoms include hard starting or no starting at all.

Possible Causes

There are many factors that may lead to this condition, some of the most common causes are:

  • Failed fuel pump
  • Failed injector
  • Defective fuel filter
  • Problem with the plugged air intake or exhaust

Other components that must be checked that must be causing the problem are:

  • Fuel composition sensor circuit malfunction
  • Low cylinder 1 injector circuit
  • Crankshaft position sensor B circuit malfunction

How to Check

Technicians usually start their diagnosis for this code by searching for leaks in the vacuum. To check for leaks, they inspect the two small vacuum hoses connected to the MAP sensor. If the hoses have never been changed with good quality silicon hose before, then there’s a good chance the hose is past it’s due.

Next, they check the rubber boot for vacuum leaks where the throttle body is attached to the motor.

Simultaneously, a lean condition is caused by a fuel issue, which means the fuel filter could be dirty or clogged or the injector is dirty, causing a bad load of fuel. Thus, fuel filter must be changed, and the tank must be cleaned using a tank or two of injector cleaner.

How to Fix

  • Repair or replace vacuum hoses
  • Repair or replace rubber boots
  • Repair or replace fuel filter or injector

Lean conditions such as Error Code 1171 are usually an easy problem to fix. Simply start with the fundamentals first before proceeding to fixing Oxygen sensors or other complicated components and issues.