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 P0170 and P0173. Following conditions must be met during the test:
- Engine coolant temperature is 176-207°F (80-97°C).
- Atmospheric temperature is 14-140°F (-10-60°C).
- If automatic transmission, selector lever is in "D" range.
- If applicable, overdrive switch is in ON position.
- If applicable, pattern select switch is in OFF position.
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.
- Start engine.
- Accelerate to 55-60 MPH.
- Drive at 55-60 MPH for 30 minutes or more (M/T: 5th gear). 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.
- Confirm DTC is not output. If DTC is output, go to appropriate DTC test in appropriate SELF-DIAGNOSTICS article.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
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.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
No obligation. See pricing before you book.