(31) Check Hose and Wiring Connections at Fuel Pump. Check that wiring connector is making contact with terminals on pump.

ON BOARD DIAGNOSTICS

The engine controller has been programmed to monitor many different circuits of the fuel injection system. If a problem is sensed with a monitored circuit often enough to indicate an actual problem, the controller stores a fault. If the problem is repaired or ceases to exist, the engine controller cancels the Fault Code after 51 vehicle key on/off cycles.

Certain criteria must be met for a fault code to be entered into engine controller memory. The criteria may be a specific range of engine RPM, engine temperature, and/or input voltage to the engine controller.

It is possible that a fault code for a monitored circuit may not be entered into memory even though a malfunction has occurred. This may happen because one of the fault code criteria for the circuit has not been met. For example, assume that one of the fault code criteria for the MAP sensor circuit is that the engine must be operating between 750 and 2000 RPM. If the MAP sensor output circuit shorts to ground when engine RPM is above 2400 RPM (resulting in a 0 volt input to the engine controller) a fault code will not be entered into memory. This is because the condition does not occur within the specified RPM range.

There are several operating conditions for which the engine controller does not monitor and set fault codes. Refer to Monitored Circuits and Non-Monitored Circuits in this section.

Stored fault codes can be displayed either by cycling the ignition key On - Off - On - Off - On, or through use of the Diagnostic Readout Box II (DRB II). The DRB II connects to the diagnostic connector in the vehicle (Figure 21 or 22).

Fig. 21 Diagnostic Connector LocationÐAA and AP

Vehicles

Fig. 22 Diagnostic Connector LocationÐAG and AJ

Vehicles

MONITORED CIRCUITS

The engine controller can detect certain fault conditions in the fuel injection system.

Open or Shorted Circuit - The engine controller can determine if the sensor output (input to controller) is within proper range. Also, the controller can determine if the circuit is open or shorted.

Output Device Current Flow - The engine controller senses whether the output devices are hooked up. If there is a problem with the circuit, the controller senses whether the circuit is open, shorted to ground, or shorted high.

Oxygen Sensor - The engine controller can determine if the oxygen sensor is switching between rich and lean once the system has entered closed loop. Refer to Modes of Operation in this section for an explanation of closed loop operation.

NON-MONITORED CIRCUITS

The engine controller does not monitor the following circuits, systems and conditions that could have malfunctions that result in driveability problems. Fault codes may not be displayed for these conditions. However, problems with these systems may cause fault codes to be displayed for other systems. For example, a fuel pressure problem will not register a fault directly, but could cause a rich or lean condition. This could cause an oxygen sensor fault to be stored in the engine controller.

Fuel Pressure - Fuel pressure is controlled by the fuel pressure regulator. The engine controller cannot detect a clogged fuel pump inlet filter, clogged in-line fuel filter, or a pinched fuel supply or return line. However, these could result in a rich or lean condition causing an oxygen sensor fault.

Secondary Ignition Circuit - The engine controller cannot detect an inoperative ignition coil, fouled or worn spark plugs, ignition cross firing, or open spark plug cables.