2010 Cadillac CTS Sedan AWD V6-3.6L Page 1125
* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System
Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an
overview of the diagnostic approach.
* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure
Instructions) provides an overview of each diagnostic category.
DTC Descriptors
DTC P0171
- Fuel Trim System Lean Bank 1
DTC P0172
- Fuel Trim System Rich Bank 1
DTC P0174
- Fuel Trim System Lean Bank 2
DTC P0175
- Fuel Trim System Rich Bank 2
Circuit/System Description
The engine control module (ECM) controls a Closed Loop air/fuel metering system in order to provide the best possible combination of
driveability, fuel economy, and emission control. The ECM monitors the heated oxygen sensor (HO2S) signal voltage, and adjusts the fuel delivery
based on the signal voltage while in Closed Loop. A change made to the fuel delivery changes the long and short term fuel trim values. The short
term fuel trim values change rapidly in response to the HO2S signal voltages. These changes fine tune the engine fueling. The long term fuel trim
values change in response to trends in the short term fuel trim The long term fuel trim makes coarse adjustments to fueling in order to re-center and
restore control to short term fuel trim. The ideal fuel trim values are around 0 %. A positive fuel trim value indicates that the ECM is adding fuel in
order to compensate for a lean condition. A negative fuel trim value indicates that the ECM is reducing the amount of fuel in order to compensate
for a rich condition.
If the ECM detects an excessively lean condition, DTC P0171 or P0174 sets. If the ECM detects an excessively rich condition, DTC P0172 or
P0175 sets.
Conditions for Running the DTC
* DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0201-P0206, P0300-P0306, P0442, P0443, P0446, P0449, P0451-P0455, P0496,
P0506, P0507, P2227-P2230, P2269 are not set.
* The engine is in Closed Loop status.
* The engine coolant temperature (ECT) is between -38 and +150掳C (-36 and +302掳F).
* The intake air temperature (IAT) is between -38 and +150掳C (-36 and +302掳F).
* The manifold absolute pressure (MAP) is between 5-255 kPa (1.45-37 psi).
* The vehicle speed is less than 134 km/h (83 mph).
* The engine speed is between 400-6,600 RPM.
* The mass air flow (MAF) is between 0.5-510 g/s.
* The barometric pressure (BARO) is greater than 70 kPa (10.2 psi).
* The fuel level is greater than 10 %.
* This diagnostic runs continuously when the above conditions have been met.
Conditions for Setting the DTC
* The average long term FT weighted average value is greater or less than a calibrated value.
* The above condition is present for approximately 3 min after the Conditions for Running the DTC have been met.
Action Taken When the DTC Sets
DTCs P0171, P0172, P0174, and P0175 are Type B DTCs.
Conditions for Clearing the MIL/DTC
DTCs P0171, P0172, P0174, and P0175 are Type B DTCs.
Diagnostic Aids
* Allow the engine to reach operating temperature. With the engine running, observe the HO2S parameter with a scan tool. The HO2S value
should vary from approximately 40 mV to approximately 900 mV, and respond to fueling changes.
* The normal Short Term FT and Long Term FT parameters should be between +10 and -10 % with 0 % the optimum, with the engine running
at operating temperature.
