P1A78 Imperial Custom Diagnostic Trouble Code

P1A78 Imperial Custom code definition:
P1A78 is a kind of OBD-II Diagnostic P-Powertrain Diagnostic Trouble Code for Imperial Custom.

P1A78 Imperial Custom is described as Intake Air Temperature (IAT) Circuit Malfunction. It's actually a general trouble code for a problem on IAT electrical circuit sensor, as it sends incorrect voltage input signals to the PCM. There are two wires dedicated for each coil; one is battery feed which usually comes from the distribution center, and the other one for the coil driver circuit from the PCM. The PCM grounds or ungrounds the circuit to activate or deactivate the coil.

Symptoms

Symptoms of a P1A78 Imperial Custom diagnostic trouble code may include:
  • Fuel pressure too high
  • Diminished fuel efficiency
  • Rich or lean exhaust
  • The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.
Place of P1A78 in engine

Possible Causes :

  • Low fuel pressure caused by a clogged filter, failing fuel pump, failed fuel pressure regulator or clogged or leaking injectors.
  • Low fuel pressure caused by a clogged filter, failing fuel pump, failed fuel pressure regulator or clogged or leaking injectors.
  • Faulty IMRC actuator relay (if equipped)

Common Misdiagnoses

  1. Exhaust Gas Recirculation System Valve 1 Problem
  2. BBV Sensor Circuit Low Voltage Problem
  3. Transmission Engaged At High Throttle Angle Problem
  4. Cruise Inhibit Control Circuit Problem
  5. TFP Valve Position Switch-Drive Without Drive Ratio Problem

Repair Processes :

Find out what kind of system you have and verify that voltage to the fuel level sensor is present at the fuel pump wiring harness. If the scan tool has that capability, and the scan tool can operate the IMRC valves, then the problem is either resolved and a simple code clearing is all that's left or a new PCM would be called for.

Process Tips

Diagnostic trouble code P1A78 Imperial Custom is not difficult to diagnose and repair. Thus, it always pays to have a qualified technician to look after your vehicle should this error code arise.

Diagnosing this code requires the engine to be in good running shape, without unmetered air entering the engine. If other codes that relates to misfiring condition, lean running or air entering the engine is present, then you must first fix those error codes before P1A78 Imperial Custom.

Fortunately, P1A78 Imperial Custom is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

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