P0170: Fuel Trim Malfunction (Bank 1)

P0170 means the fuel trim values on bank 1 have exceeded the normal correction range. The ECU can no longer properly compensate for a rich or lean condition by adjusting fuel delivery. This indicates a persistent air-fuel mixture problem that needs investigation.

P0170 is a fuel system-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0170 and illuminates the check engine light.

If your vehicle has triggered P0170, you may notice one or more of these symptoms:

• Check engine light on
• Poor fuel economy
• Rough or unstable idle
• Hesitation or stumbling during acceleration
• Possible misfires under load
• Failed emissions test

Here are the most common causes of P0170, ranked by how likely they are to be the culprit:

Generally yes, for short-term driving. You can drive to a workshop but expect reduced fuel economy and possible rough running. If accompanied by misfires or strong exhaust smell, limit driving.

Follow these steps to pinpoint the root cause of P0170:

1. Use a scan tool to read short-term and long-term fuel trims for bank 1. Values beyond +/- 25% indicate a significant air-fuel ratio problem. Positive trims mean lean, negative trims mean rich
2. If fuel trims are positive (lean), perform a smoke test or propane enrichment test to find vacuum leaks. Check intake manifold gaskets, PCV hoses, brake booster line, and all vacuum connections
3. Inspect and clean the MAF sensor with dedicated MAF cleaner spray. A contaminated MAF underreports airflow, causing lean fuel trims
4. Check fuel pressure with a gauge. Low pressure causes lean trims, high pressure causes rich trims. Compare to manufacturer specifications
5. Monitor the upstream O2 sensor data. If it is sluggish or stuck, it may be providing incorrect feedback that forces the fuel trims out of range
6. If trims are negative (rich), check for leaking injectors by performing a fuel injector balance test or checking for fuel smell in the oil

Repair costs for P0170 vary depending on the root cause and your vehicle. Here are typical estimates:

P0170 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:

These codes are often seen alongside P0170 or indicate related issues: