Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Fuel Trim Monitor
This monitor applies to DTCs P0171 and P0172. Following conditions must be met during the test:
- Engine coolant temperature is 176-207°F (80-97°C).
- Atmospheric temperature is 14-140°F (-10°C to 60°C).
- Selector lever is in "D" range (A/T).
Monitor takes about 35 minutes to complete. To run monitor, use illustration. See Fig 1 . Perform steps as follows:
- Remove all test equipment from vehicle and install all components and connectors that were removed or disconnected during testing.
- Warm engine to normal operating temperature. Turn ignition off.
- Start engine and accelerate vehicle to 55-60 MPH. Use 5th gear on M/T.
- Drive at 55-60 MPH for 30 minutes or more. During this period DO NOT drive at constant speed for more than 120 seconds. Carry out gradual deceleration and acceleration within every 120 second time frame. Depressing brake pedal is okay, but avoid abrupt braking.
- Return vehicle to shop and turn ignition off. Recheck for DTC(s). If any DTC(s) is set, diagnose affected DTC(s). See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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