P0088 is a common OBD2 trouble code that can occur in the Ford Flex. In layman’s terms, it indicates that your SUV’s fuel pressure is too high.
While P0088 is a generic code, repair steps will vary depending on your Flex’s model year, engine type, and how it regulates fuel pressure.
P0088 Definition: Fuel Rail/System Pressure – Too High
P0088 is a generic powertrain code that indicates a fuel pressure issue. This code is set when your Flex’s PCM detects too much pressure in the fuel system.
Fuel Rail/System Pressure
The purpose of the pressure monitoring system is to help the engine run by monitoring the fuel pressure from the fuel injection system. Too much fuel can lead to just as many problems as no fuel.
Too High
If the fuel pressure is too high (the voltage value coming from the fuel pressure sensor is over the maximum value), it signals your Flex’s PCM to display code P0088. Several components make up the fuel system. If any of them are faulty, it could cause a code P0088.
The main components that can fail and cause P0088 are the fuel pump, fuel pressure regulator, and fuel pressure sensor. Knowing how your SUV’s fuel pressure is regulated can help you figure out the faulty component.
There are two ways that an engine can have its fuel pressure regulated.
- The first way is to use a fuel pressure regulator, which returns the extra pressure to the fuel tank.
- The other way is that the fuel pressure is regulated by the fuel pressure sensor, as it works with the PCM. The fuel pump can adjust to the needs of the engine directly, with no regulator needed. The fuel pressure sensor signals the pressure in the fuel rail to the PCM. If it’s not working correctly, the engine may stall or run rough.
P0088 Symptoms: Ford Flex
There will almost ALWAYS be symptoms associated with P0088 if the fuel pressure is incorrect. There may not be any symptoms if the fuel pressure sensor is bad.
Here are the common symptoms associated with P0088 in the Ford Flex:
- Slow/no start
- Decreased fuel mileage
- Misfiring (you’ll likely see code P0300, focus on P0088 first)
- Fouled spark plugs
- Stalling
- Black exhaust smoke
P0088 Causes
Here are the most common causes of P0088 in the Ford Flex:
- Bad fuel pressure regulator
- Bad fuel pressure sensor
- Bad fuel pump
- Wiring issues at the fuel pressure sensor
- PCM
Ford Flex P0088 Diagnosis
While several things can cause the P0088 code in the Ford Flex, here’s a good order to diagnose them in:
Inspect the Fuel Pressure Sensor Wiring
Start here (particularly if your Flex is running fine).
Take a look at the fuel pressure sensor wiring. Make sure that it is not burnt, cracked, or frayed. Due to its location, damage to the harness is very common. It’s not uncommon for a rodent to nest around the intake, particularly in the wintertime.
Make sure that the harness is plugged into the sensor tightly and that there are no damaged pins inside the connector. If there are, you’ll need to repair or replace the harness.
Check the Fuel Pressure
Be careful when checking your Flex’s fuel pressure. It’s always best to do it with the engine cold. Make sure you have a fire extinguisher ready in case the fuel sprays. Do not connect or disconnect the fuel pressure gauge with the engine on.
The next course of action when diagnosing P0088 is to test the actual fuel pressure at the fuel rail. You’ll need a manual fuel pressure testing gauge. That’s not a tool that most Shadetree mechanics have, you can usually rent one or borrow one from the local parts store.
You’ll need to look up the exact fuel pressure for your vehicle and engine combination. If the fuel pressure checks out, you likely have a bad fuel pressure sensor.
If the fuel pressure is too high, you’ll need to replace the fuel pressure regulator.
Check the Fuel Pump
A returnless fuel pump can cause P0088. You’ll need to verify what type of fuel system your particular Ford Flex has.
Using a multimeter, check the resistance of the fuel pump by connecting the positive lead to the positive terminal on the pump and the negative lead to the negative terminal.
Conclusion
Fixing P0088 in the Ford Flex involves determining whether or not the fuel pressure is really too high or if the sensor is bad. If the pressure is too high, it can only be a few things that cause the issue.