Powertrain Controls - ECM/PCM

DTC 43 Chart:

Heated Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION
The PCM provides a 0.45 volt reference signal to the HO2S on CKT 412. When the HO2S is cold, below 200°C (392°F), the HO2S signal voltage will be around 0.45 volt and the PCM will keep the system open "0pen Loop" operation. When the HO2S is warm, above 200°C (392°F), the HO2S will swing from rich to lean rapidly, at least one swing every seconds, if the PVCM is in good control of the air fuel mixture. DTC 43 is designed so that if the HO2S stays at a rich voltage for more than 50.3 seconds during the test conditions, DTC 43 will set

DTC 43 WILL SET WHEN
- DTCs 14, 15, 16, 21, 22, 26, 27, 31, 32, 34 and 119 are not set.
- Throttle switch open.
- TP angle between 5.4° and 25°.
- Coolant temperature above 82.5°C.
- Oxygen sensor ready.
- Engine speed 800 RPM or greater.
- Low coolant level and engine overheat not present.
- Traction control not active.
- The Bank2 HO2S voltage is between 0.6 volt and 0.95 volt for more than 50.3 seconds.
- MAP greater than 20.2 kPa.

ACTION TAKEN (PCM WILL DEFAULT TO)
- With current DTC 43 set, the PCM will illuminate the Malfunction Indicator Lamp (MIL) ( Service Engine Soon).
- PCM enables evaporative emission control solenoid if DTC 45 is also set.

DTC 43 WILL CLEAR WHEN
The fault no longer exists and ignition is cycled "OFF" and "ON."

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. If DTC 17 is also set, diagnose it first because an oxygen sensor not ready can cause other emission related problems.
2. If the oxygen sensor is operating correctly, voltage will fluctuate below 0.6 volt. A rich sensor/condition will cause the voltage to remain above 0.6 volt. If less than 0.95 volt is measured, the PCM and CKT 412 are OK.
3. Checks for sort to voltage on CKT 412.

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 43 may have been set. If the conditions for DTC 43 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 43 may be set. Refer to "Fuel System Diagnosis," Chart A-7. Chart A-7 Fuel System Pressure Test

Rich injector
Perform "Injector Balance Test," Chart C-2A. Chart C-2A Injector Coil Balance Test Procedure

Leaking injector
Refer to "Fuel System Diagnosis," Chart A-7. Chart A-7 Fuel System Pressure Test

Check for fuel contaminated oil.

HO2S contamination
Inspect Heated Oxygen Sensor (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.

HEI shielding
An open ground CKT 453 may result in EMI or induced electrical "noise." 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.

TP sensor
An intermittent TP sensor output will cause the system to go rich, due to a false indication of the engine accelerating.

EGR sensor
An EGR staying open (especially at idle) will cause the Oxygen Sensor (HO2S) to indicate a rich HO2S signal and this could result in a DTC 43.