P0170

What it means

P0170 is the generic code for a fuel trim malfunction on Bank 1, the side of the engine with cylinder number one. The engine control unit saw the long-term and/or short-term fuel trim needing to correct by more than its allowed limit, either adding or removing fuel, to hold the target air-fuel ratio. The code does not say whether the mixture is lean or rich, so freeze frame and live trim data are needed to find out.

Symptoms

• Engine warning light on
• Rough or unstable idle
• Hesitation or poor acceleration
• Poor fuel economy
• Occasional misfires or stalling
• Smell of fuel or exhaust fumes

Possible causes

• Vacuum leak or unmetered air entry (split hose, intake gasket, brake servo hose, loose intake pipe)likely
• Faulty or contaminated mass airflow sensor, or air leak after the sensorlikely
• Exhaust leak upstream of the Bank 1 oxygen sensor giving false lean readingspossible
• Fuel delivery fault on Bank 1 such as a clogged, leaking or sticking injector, or low fuel pressure from a weak pump or blocked filterpossible
• Faulty or slow Bank 1 upstream oxygen or air-fuel ratio sensor, or damaged wiring and connectorspossible
• Crankcase ventilation or evaporative purge valve fault letting in extra air or fuel vapourpossible
• Engine mechanical problem such as a burnt valve or low compression on Bank 1rare

How to diagnose

1. Read all stored and pending codes and note the freeze frame data, including fuel trims, engine load, coolant temperature and rpm
2. Check live short-term and long-term fuel trims at idle and at about 2500 rpm to see whether the correction is lean (positive) or rich (negative) and whether it changes with load
3. Visually inspect intake pipework, vacuum hoses, the crankcase breather system and air filter housing for splits, loose clips and disconnected connections
4. Inspect the exhaust upstream of the Bank 1 oxygen sensor for leaks, and inspect sensor wiring and connectors for damage or contamination
5. Compare mass airflow sensor readings with expected values at idle and check for contamination, noting the correct procedure varies by model
6. Check for a vacuum or intake leak with a smoke test
7. Test fuel pressure and volume against the manufacturer's specification, and check injector operation on Bank 1
8. Check oxygen sensor response in live data and test the purge valve operation, following the procedure for the specific engine

How to fix

• Repair or replace any leaking vacuum hose, intake gasket or loose intake connection
• Clean or replace the mass airflow sensor if it is faulty or contaminated
• Repair exhaust leaks ahead of the oxygen sensor
• Clean or replace faulty injectors, or replace a failing fuel pump or fuel filter where the system has one serviceable
• Replace a faulty Bank 1 oxygen or air-fuel ratio sensor and repair damaged wiring or connectors
• Replace a faulty purge valve or crankcase ventilation component, then confirm fuel trims return to normal

Can I keep driving?

Nearby codes

• P016FGenericClosed Loop Fuel Pressure Control At Limit - Pressure Too Low
• P0171GenericSystem Too Lean Bank 1