Powertrain Controls - ECM/PCM
DTC 45:
Heated Oxygen Sensor Schematic:
CIRCUIT DESCRIPTION
The Heated Oxygen Sensor (HO2S) has 450 millivolts applied to it by the Powertrain Control Module (PCM) on circuit 412. This voltage may vary slightly when measured with a 10 megohm (minimum) impedance DVOM. As the HO2S warms and becomes active, it also produces a voltage which will vary from 100 to 1000 millivolts. The PCM then detects whichever voltage is greater at the HO2S signal input. If the HO2S voltage is less than the 450 millivolts reference, the sensor acts as a ground and functionally reduces the voltage level at the input. This effect causes the Tech 1 scan tool to display a 100 to 1000 millivolt operating range. The heater in the HO2S allows for faster sensor warm-up and better temperature stabilization during engine operation.
DIAGNOSTIC TROUBLE CODE (DTC) 45 WILL SET WHEN
Vehicle is operating in "Closed Loop," circuit 412 is above 750 millivolts, throttle angle is between 6% and 20%, condition present for greater than 60 seconds.
ACTION TAKEN (PCM) WILL DEFAULT TO
Vehicle will operate in "Open Loop" and Malfunction Indicator Lamp (MIL) will become illuminated.
DTC 45 WILL CLEAR WHEN
A current DTC 45 will clear when the HO2S signal voltage falls below the calibrated rich exhaust voltage threshold. A History DTC 45 will clear after 50 consecutive ignition key cycles without a current DTC 45 being stored.
DIAGNOSTIC AIDS
Using the Tech 1 scan tool, observe the long term fuel trim values at different RPM and air flow conditions. The Tech 1 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 45 may have been set. If the conditions for DTC 45 exist, the long term fuel trim values will be around 115.
Fuel Pressure
System will go rich if pressure is too high. The PCM can compensate for some increase. However, if it gets too high, a DTC 45 may be set. Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart A-7. Related Tests, Information and Procedures
Rich Injector
Perform "Injector Balance Test, Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart C-2A. Chart C-2A Fuel Injector Balance Test
Leaking Injector
Refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart A-7. Related Tests, Information and Procedures
Crankcase Oil
Check for fuel contaminated oil.
Heated Oxygen Sensor Contamination
Inspect HO2S for silicone contamination from fuel, or use of improper RTV sealant. The sensor may have a white, powdery coating and result in a high but false signal voltage (rich HO2S signal indication) The PCM will then reduce the amount of fuel delivered to the engine, causing a severe surge driveability problem.
Electronic Ignition
An open ground (ref. low) circuit 453 may result in Induced Electrical Noise or Electromagnetic Interference (EMI). The PCM looks at this noise as reference pulses. The additional pulses result in a higher than actual engine speed signal. The PCM then delivers too much fuel, causing system to go rich. Engine tachometer will also show higher than actual engine speed, which can help in diagnosing this problem.
EVAP Canister Purge
Check for fuel saturation. If full of fuel, check canister control and hoses.
Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.
Throttle Position (TP) Sensor
An intermittent TP sensor output will cause the system to go rich, due to a false indication of the engine accelerating.
Exhaust Gas Recirculation (EGR)
An EGR staying open (especially at idle) will cause the HO2S to indicate a rich HO2S signal and this could result in a DTC 45.
Circuit 412
Shorted to voltage will set DTC 45, because it simulates a rich condition.