• The Ford Motor Co. has utilized multiple control systems within various engines since 1984. Upon diagnosing error code 334, you identified a continuous memory code stored in the Electronic Engine Control system, version IV. Diesel engines use the same codes with slightly different implications. The best course of action is to clear the code, run the engine for 30 miles and retest to verify code 334 implies an error in the system.
  
  

Code 334 Defined

• Code 334 in the EEC-IV system implies that the EGR valve, when closed, produced higher voltage than expected. The code does not imply damage or malfunction. It only means that the voltage read did not fall within the acceptable parameters and the EEC-IV triggered a response. In a diesel engine, the code 334 implies an injection control system response time fault. For diesels, the Diagnostic Trouble Code 334 measures desired injection control pressure versus measured, and looks for a noticeable pressure difference of 1,300 PSI.
  
  

Causes

• The most likely cause of the code 334 in the EEC-IV system is the EGR valve was open while the engine was stabilized and at idle sometime during vehicle operation. The open valve would allow too high a voltage to be read, triggering the sensor.
  
  

Causes (Diesel Engines)

• Low oil, bad oil or aerated oil triggers the DTC 334 in diesel engines. The code could also be generated by a defective Injection Pressure Regulator or leaks in the Injection Control Pressure system. The wiring to the system may have a poor connection, which would also trigger the code, or it may be a defective hydraulic pump.