OBD codes / P0174 / Toyota Highlander
P0174 on a Toyota Highlander
System Too Lean (Bank 2)
3.0L 1MZ-FE, 3.3L 3MZ-FE, and 3.5L 2GR-FE V6; bank 2 is the firewall side.
What P0174 usually means on a Highlander
P0174 is the bank 2 lean code and appears only on V6 Highlanders. It means the rear (firewall-side) cylinder bank is running lean. On its own it usually points to something specific to that bank — a cracked rear PCV hose or a leaking rear intake gasket. When it comes with P0171, the cause is generally shared between banks, such as a dirty MAF or low fuel pressure.
Most likely causes on this model
- Bank 2 vacuum leak
A split rear PCV hose or a leaking rear intake gasket leans just the firewall-side bank.
- Dirty MAF (with P0171)
Two lean banks at once usually trace back to one contaminated MAF.
- Failing bank 2 AF sensor
That bank's rear Denso sensor is usually original and gets lazy with age.
- Low fuel pressure
A weak pump pulls both banks lean under load; check pressure when trims climb on every bank.
What it costs on a Highlander
A standalone P0174 means chasing a rear-bank vacuum leak, which is fiddly because the hoses tuck behind the intake on the transverse V6, so budget for diagnostic time. A cause it shares with P0171 is easier to pin down. A smoke test is the quickest route to the leak.
Year, engine and mileage change the answer. Get a diagnosis for your Highlander — it weighs these causes against your exact configuration and real complaint data.
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Toyota Highlander problems & recalls by year
Based on widely reported patterns for this model; individual causes vary by year, engine and history. Generic P0174 behavior is covered on the main P0174 page. Confirm with a scan tool before buying parts.