Question about 2006 Cadillac STS
• DTC P0171 Fuel Trim System Lean Bank 1
• DTC P0174 Fuel Trim System Lean Bank 2
The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop, the ECM determines fuel delivery based on sensor signals without oxygen sensor (O2S) input. During Closed Loop, the O2S inputs are added and used by the ECM to calculate short and long term fuel trim (FT) fuel delivery adjustments. If the O2S indicates a lean condition, FT values will be above 0 percent. If the O2S indicate a rich condition, FT values will be below 0 percent. Short term FT values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long term FT makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. If the ECM detects an excessively lean condition, DTC P0171 or P0174 sets.
• Excessive resistance in the fuel injector ignition 1 voltage circuit or the fuel injector control circuit may cause the following symptoms:
- Lean condition
- Rough idle
• The system will go lean if an injector is not suppling enough fuel.
• A lean condition could be present during high fuel demand.
• A malfunctioning MAF sensor can cause this DTC to set. Refer to DTC P0101 .
• Review the Failure Records with a scan. If an intermittent condition is suspected, refer to Intermittent Conditions .
This diagnostic procedure supports the following DTCs:
• DTC P0420 Catalyst System Low Efficiency Bank 1
• DTC P0430 Catalyst System Low Efficiency Bank 2
This code could mean the catalytic converter on that bank has failed .
Causes of lean condition trouble codes P0171 P0174 GM 5 3L
P0420 P0430 catalytic converter catalyst inefficiency code diagnosis
Posted on Mar 28, 2018
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Posted on Jan 02, 2017
The P0420 code is a Catalytic converter efficiency code check the compression.Swap the #1 injector to a different location to see if the code follows.Test the coilpak. A cracked exhaust manifold is the most likely cause p0171 and 0174 Induction air leaks, vacuum or some kind fuel restriction, weak fuel pump, restricted fuel filter etc.You also could have an exhaust leak near the upstream o2 sensor. If youtake it in they will probably use smoke to find out where the leak is.
Posted on Apr 22, 2009
0174 is system too lean, right bank. 0420 is catalyst sytem efficiency below threshold, left bank. fix would be either oxygen sensor or catalytic converter replacement possibly would need both. note: this veh would possibly have up to 4 oxygen sensors, but cause of problem would be the ones coming off manifolds before the catalytic converter possibly in manifold or y-pipe/down pipe.
Posted on Aug 27, 2012
The recommended repair for both the P0171 and P0174 codes is to clean the MAF sensor. Ensure you use the proper cleaning solution, as there are many that will damage the sensor. Buy a cleaner that is made specifically for MAF sensors. The P0420 code will probably clear up if the MAF sensor clears the other two codes.
Posted on Nov 13, 2015
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