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P1151: Lack of Upstream Heated Oxygen Sensor Switch Sensor Indicates Lean Bank 2

Unlike many OBD trouble codes, P1151 is only applicable to Ford vehicles. This guide isn’t applicable to other automotive brands. Wondering, "how do I fix trouble code P1151?" Discover what this trouble code is communicating and troubleshoot common causes and solutions to restore your Ford vehicle.

What Is a Ford Trouble Code P1151?

This trouble code is signaled by your heated exhaust oxygen sensor, or HO2S. This sensor is used to test the amount of oxygen to ensure an accurate air/fuel ratio. A failed test means there isn’t enough air mixing with your fuel.

This could be the result of improper air intake. However, it also could be a sign of too much fuel being injected. For many cases, it’s simply a sign of an electrical issue with your HO2S or powertrain control module.

What are the Symptoms of P1151?

The unique issue with your P1151 problem is that it could be caused by a wide range of issues. Because of the many interrelated parts, you’ll need to check your electrical, induction system, PCV system, base engine, EGR system, and fuel system for a potential cause. However, the issue is typical an electrical issue in one or more of these systems, so you’re unlikely to notice any performance issues. You’ll simply see your Check Engine light illuminated.

A lack of symptoms doesn’t mean that you can ignore trouble code P1151. This sensor being triggered could be the result of a much more serious issue with your engine, fuel system, or induction system, so it’s important to look for the cause and find a solution.

Typical Causes

First, inspect your electrical system to determine if there’s an issue. Your powertrain control module or HO2S could be damaged, wiring connectors could be loose, or there could be water in the harness connector. Any other these would result in an incorrect HO2S reading and trouble code P1151.

The next system to check is your fuel system. Leaking fuel injectors, low fuel, or too much fuel pressure could all result in this trouble code. Carefully inspect your fuel system to find any damaged or contaminated components that would cause an imbalance of fuel and air.

A range of minor issues throughout the other systems could also be the cause of this trouble code. An air leak after your mass air flow sensor or a leaking gasket in your EGR system could be the cause. Improperly seating your engine oil dipstick could also result in this error code.

Your base engine could be experiencing cylinder compression, issues with cam timing or have an oil overfill. Any exhaust leaks near the HO2S would also result in error code P1151. Each of these causes need to be carefully checked in order to find the solution. If your error code has been on for some time, it could result in multiple causes.

How to Fix P1151

Work through your many causes in order to find a prompt repair solution. Some issues, like a contaminated fuel injector or an improperly seated dipstick, require a little adjustment. Others, like a damaged powertrain control module or leaking EVR, require more extensive repairs.

Once you determine the cause and solution, you have a better understanding of what does the code P1151 mean? After you’ve repaired the damaged component, clear your code and check to see if that was the only issue. If your code reappears, continue to look for additional causes and make repairs as necessary.

Don’t wait until you begin to experience performance issues. Search for the issue and be sure that you’ve properly cleared trouble code P1151 in order to avoid further damage to essential components in your fuel system, base engine, or EGR system.

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