P1151 is a diagnostic trouble code that applies to vehicles manufactured by Ford. Fault codes starting with P1XXX were reserved for manufacturers. This code occurs when the bank 2 O2 sensor fails a diagnostic test twice in a row.
DTC P1151 is usually caused by a bad oxygen sensor, fuel injector, or vacuum leak. But there may also be other causes.
….most likely it is the oxygen sensor itself that caused the P1151.
Definition and how to find the correct O2 sensor
Ford chose P1151 to indicate “Lack of Upstream Heated Oxygen Probe Switch | Lean Bank 2“
Updraft– The upstream oxygen sensor is the sensor located before the catalyst. It is usually bolted to the exhaust manifold or right after it.
Bank 2– Bank 2 is the part of the engine with the second cylinder. It is only applicable to engines with a “V” configuration. Bank 2 is pretty easy to find. Here is a short article on how to find which side of the engine has bank 2. It will open in another tab.
Once you find it come back here and we will try to find out the cause of P1151 in your vehicle.
Typically, there will not be any symptoms associated with P1151 (other than the check engine light).
Causes of P1151
- Defective O2 sensor (Bank 2 Sensor 1): Look above if you need help locating it.
- vacuum leak
- Fuel system problem: Fuel pressure may be too high or too low. Or there could be a clogged fuel injector.
- Faulty air mass sensor
- PCM (Vehicle Computer)
P1151 Diagnosis and repair
There are a few things you can do at home to detect the cause of P1151 and repair it. Here they are in order of likelihood/ease of verification.
Faulty O2 sensor wiring
The upstream oxygen sensor on almost any car is fairly easy to find. Once you know where bank 2 is, just follow the exhaust manifold until you find the oxygen sensor.
Inspect the wiring harness to see if it has been damaged in any way. Look at the contacts where they connect to the sensor itself. Due to the location of an oxygen sensor in hot exhaust components, the wiring harness fails more than a typical wiring harness would.
Bad oxygen sensor
P1151 is activated because the oxygen sensor has failed a test. Specifically, the test is designed to verify that the oxygen sensor has the appropriate output voltage and response speed. You must fail this test twice for the check engine light to come on.
With this in mind, knowing that the oxygen sensor has failed this test, it is most likely the oxygen sensor itself that is bad.
The system could have a vacuum leak. Determining where there is a vacuum leak can be easy. Here is a great video on exactly how to do it.
The fuel system itself can cause P1151.
Fuel pressure may be too low. The cause would be a clogged fuel filter, weak fuel pump, or bad fuel pressure regulator. But, if the fuel pressure is too low, P1131 will likely also appear (same code, just on the other side of the engine).
Given the above, if the fuel system is to blame, it is likely a problem with a fuel injector.
A clogged fuel injector can tilt the mixture in bank 2, without affecting bank 1.
Ford P1151 Overview
As you can see, P1151 can be caused by a host of problems. The cause is most likely a faulty oxygen sensor, fuel injector, or vacuum leak.
Good luck diagnosing your vehicle. If there is anything you want to add, please leave a comment.