DTC 64

DTC 64 Chart Oxygen Sensor Circuit:

Wiring Diagram Oxygen Sensor Circuit:

Circuit Description:

The ECM supplies a voltage of about 450 mV between terminals "D6" and "D16". (If measured with a 10 megohm digital voltmeter, this may read as low as 320 mV.) The oxygen sensor varies the voltage within a range of about 1000 mV if a rich O2 Sensor signal is indicated, down through about 10 mV if a lean O2 Sensor signal is indicated.

The sensor is like an open circuit and produces no voltage when it is below 315°C (600°F). An open sensor circuit or cold sensor causes "Open Loop" operation.



1. DTC 64 will set if:

^ Signal voltage remains below 200 mV for 50 seconds.
^ System is operating in Closed Loop."


Diagnostic Aids:


Using the scan tool, observe the long term fuel trim at different RPM and air flow conditions. The scan tool also displays the fuel trim cells, so the long term fuel trim values can be checked in each of the cells to determine when the DTC 64 may have been set. If the conditions for DTC 64 exist, the long term fuel trim values will be around 160.


Check the following possible causes:

^ Oxygen Sensor Wire - Sensor pigtail may be mis-positioned and contacting the exhaust manifold. Check for ground in wire between connector and sensor.

^ Lean Injector(s). Testing and Inspection

^ Fuel Contamination - Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can set a DTC 64.

^ Fuel Pressure - System will be lean if fuel pressure is too low. It may be necessary to monitor fuel pressure while driving the vehicle at various road speeds and/or loads to confirm. Related Tests, Information and Procedures

^ Exhaust Leaks - If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor. Vacuum or crankcase leaks can cause a lean condition.

^ AIR System. Make sure air is not being directed to the exhaust ports while in "Closed Loop." If the long term fuel trim value goes down while squeezing air hose to right side exhaust ports, see chart C-6 Testing and Inspection

^ If DTC 64 is intermittent, - Intermittent Malfunctions

^ A cracked or otherwise damaged 02 Sensor may set an intermittent DTC 64.