Lack of HO2S Switch — Sensor Indicates Lean (Bank 2)
2009-2012 Ford Flex 3.5L V6
Description
The upstream heated oxygen sensor on Bank 2 is not switching and indicates a persistent lean condition. This is the Bank 2 counterpart of P1131 and is extremely common on Ford V6 and V8 engines. When both P1131 and P1151 appear together, the cause is typically a vacuum leak or dirty MAF sensor affecting both banks.
Symptoms
- Check Engine Light
- Rough idle
- Poor acceleration
- Increased fuel consumption
- Hesitation
Common Causes
- Vacuum leak past the MAF sensor (when paired with P1131)
- Faulty upstream O2 sensor Bank 2 (when appearing alone)
- Dirty MAF sensor
- Low fuel pressure
- PCV valve or hose leak
- Cracked intake manifold plenum gasket (4.2L V6)
- Intake manifold runner gasket leak
Diagnostic Steps
- If P1131 is also present, focus on common causes (vacuum leaks, MAF)
- If only P1151, suspect O2 sensor Bank 2
- Check PCV hose and valve cover connections
- Clean MAF sensor
- Smoke test for vacuum leaks
- Check fuel pressure
Repair Notes
If both banks show lean, repair vacuum leaks or replace MAF. If single bank, replace O2 sensor Bank 2.
Related Codes
Other Powertrain Codes
- P0001Fuel Volume Regulator Control Circuit/Open
- P0002Fuel Volume Regulator Control Circuit Range/Performance
- P0003Fuel Volume Regulator Control Circuit Low
- P0004Fuel Volume Regulator Control Circuit High
- P0010Intake Camshaft Position Actuator Circuit/Open Bank 1
- P0011Intake Camshaft Position Timing Over-Advanced Bank 1
- P0012Intake Camshaft Position Timing Over-Retarded Bank 1
- P0013Exhaust Camshaft Position Actuator Circuit/Open Bank 1
- P0014Exhaust Camshaft Position Timing Over-Advanced Bank 1
- P0015Exhaust Camshaft Position Timing Over-Retarded Bank 1
P1151 on Other Vehicles
Common Questions
What does code P1151 mean on a 2009-2012 Ford Flex?
P1151 stands for "Lack of HO2S Switch — Sensor Indicates Lean (Bank 2)". The upstream heated oxygen sensor on Bank 2 is not switching and indicates a persistent lean condition. This is the Bank 2 counterpart of P1131 and is extremely common on Ford V6 and V8 engines. When both P1131 and P1151 appear together, the cause is typically a vacuum leak or dirty MAF sensor affecting both banks.
What are the symptoms of P1151 on a Ford Flex?
Common symptoms of P1151 include: Check Engine Light, Rough idle, Poor acceleration, Increased fuel consumption, Hesitation.
What causes P1151 on a 2009-2012 Ford Flex?
Common causes of P1151 include: Vacuum leak past the MAF sensor (when paired with P1131), Faulty upstream O2 sensor Bank 2 (when appearing alone), Dirty MAF sensor, Low fuel pressure, PCV valve or hose leak, Cracked intake manifold plenum gasket (4.2L V6), Intake manifold runner gasket leak.