Toyota P1200 Powertrain – Manufacturer-controlled DTC “fuel pump relay”
Over time, the control unit or its relay can become worn, have foreign matter creep inside the plug, or just fail from age and wear and tear. The solution, of course, is to replace the fuel pump and controller, which often requires that the fuel tank be dropped (removed), though many Toyotas will have easy access to the fuel tank’s pump and relay by removing the lower part of the rear seat or from an access point in the cargo area.
Before replacing that fuel pump, however, other tests can be quickly performed that may save the trouble.
Another common issue, especially with age, is faulty wiring from the fuel pump to the engine control module (ECM, or “computer”). The simplest way to test this is to connect a meter to the circuit starting at the fuel pump and trace it back to the fuse box and ECM. If there is any break, you have a problem in the wiring you’ll need to locate and fix.
The last problem, which is more rare, is a problem in the ECM or ECU itself. If your ECM is giving trouble codes for a variety of systems or for things other than the fuel system – as well as the P1200 – then you are more likely to have ECU issues. These can be tested, which is expensive, or the ECU can be replaced – also often expensive. Either way, though, you will continue to have problems and they will likely get worse if you do not diagnose and fix this issue.
Most mechanics will recommend testing the fuel circuit first, then replacing the fuel pump before deciding on the computer unless the ECM issue is very obvious. This is for budget reasons. A fuel circuit check can be a half hour diagnostic fee, a fuel pump replacement may be just a couple of hundred dollars or so, but an ECM diagnostic or replacement can run several hundred dollars and have the car out of commission for several days.
The majority of the time, though, a P1200 code is going to be a fuel pump issue and should be relatively easy to get repaired.
Author Jason Lancaster is a long-time Toyota enthusiast working with Olathe Toyota Parts Center, a website offering discounted OEM Toyota parts online. Jason also writes for Toyota Parts Blog, a website for Toyota owners.