Error Code P0089 is usually a mechanical fault which, most of the time, can be attributed to the defective electronic fuel pressure regulator or it can be a case of faulty fuel pump. Other most common causes include:
Clogged fuel filter or pinched or restricted fuel lines
Low fuel condition
Faulty fuel pump
Defective fuel rail sensor
Damaged, open or shorted wires (corroded wires)
Damage in electrical connectors
Error on fuel pump output
Qualified mechanics start their diagnosis by hooking up their advanced level scan tool to the PCM. Any error code present will have its own freeze frame data, which includes any info that tells mechanic what circumstances triggered the PCM to set the code. This includes information about the vehicle’s speed, RPM, coolant temperature, etc.
Then, the codes will be cleared and the vehicle will be taken for a test drive.
When the code returns, the mechanic will then conduct a visual inspection of the vehicle and look for signs of damage, restriction or leaks along the fuel lines and fuel pressure regulator.
If all seems well upon visual inspection, the vehicle will now be tested for test port. This is where the mechanic will check the fuel pump output using his scan tool. He will also test the operation of fuel pressure regulator.
How to Fix
The most common fixes for this error code are:
Replace or repairing the damaged or restricted fuel lines
Replace fuel pressure regulator
Replace clogged filters or screens
Replace failed fuel pump
Did the dealers do a fuel pressure check? Or was this just an information fishing expedition? If the latter, keep in mind that you were likely talking to a service writer; most of whom would have no idea anyway. Even if you found one with what could be called “the answer” they may not divulge it as they are not in the business of providing self-help.
I don’t think this car uses a fuel pressure regulator. It uses a fuel pressure sensor which is a bit different and is electronically operated. Ford has used them for 20 or so years now.
Just carrying theorizing a bit further, what about the possibility of a weak fuel pump or lowered fuel pressure due to a partially clogged fuel filter? Maybe the fuel volume is just not high enough to handle the increased engine load due to climbing grades. To me, a fuel pressure check is step one.