A Chevy Silverado with a P0171 Code is having an issue with the Air/Fuel ratio going into the engine.
When troubleshooting a P0171 code, be sure to look for other codes that will help to troubleshoot the problem.
For example, if you have a P0171 code along with a P1101 MAF air flow sensor, the MAF sensor is likely the issue.
What is a Chevy Silverado P0171 Code
An OBDII P0171 code is “System Too Lean (Bank 1)”.
Some scan tools will also report the generic message “Fuel Trim System Lean Bank 1”.
The ECM sees an issue with the Air/Fuel ratio going into the cylinders on Bank-1.
Bank-1 is the side of the engine with the number-1 cylinder, which is the right side of the engine for a 5.3L engine.
How to Troubleshoot a Chevy Silverado with a P0171 Code
The first step to diagnosing a P0171 Code is to read the fuel pressure PSI.
Chevy makes it easy to read the PSI with a fuel pressure gauge which is a low-cost tool.
Auto parts stores often loan out fuel pressure gauges with a deposit if they will only be used once.
To measure the full PSI, attach the fuel pressure gauge to the shrader port on the fuel rail.
Once it is attached, the gauge will read the fuel pressure when the key is on, or the engine is ruing.
What is the Fuel Pressure PSI for a Chevy 5.3L Engine?
A Chevy 5.3L Engine is rated for a fuel pressure of 55 to 62 PSI.
If the pressure drops below 55 PSI, the engine will start to have a lean fuel issue.
The engine may still run depending on how low the pressure is but if the pressure is below 55 PSI, it should be fixed.
Most Common Causes and Fixes Chevy Silverado 5.3L P0171 Code: System Too Lean (Bank 1)
- Fuel Pressure Regulator
- Fuel Filter
- Fuel Pump
- Vacuum Leak
- Dirty or Bad MAF Sensor
- Oxygen Sensor
- Faulty Fuel Injector
The fuel pressure regulator is located on the side of the 5.3L engine at the fuel rail.
A small vacuum hose is attached to it, and they commonly leak out the vacuum tube when they go bad.
To check it, remove the small vacuum hose, and with the engine running, see if any fuel comes out of the unit.
If fuel spits out of the port, the regulator is bad.
They can also fail and not spit fuel out, but it is common that they do leak out gas when bad.
A clogged fuel filter can cause many issues, including low fuel pressure.
Fuel filters should be regularly changed, and swapping them out will quickly rule it out as the problem.
A weak or failing fuel pump can also cause fuel pressure issues.
If everything else is checked and there is still low pressure, then the fuel pump is likely bad.
It can be tested to see if it has failed, with most mechanics replacing it when all else has been checked.
A vacuum leak can cause issues and a P0171 Code.
There are several methods for finding a vacuum leak, such as spaying a liquid where the leak is thought to be to see if the engine idle changes.
The method I prefer is the smoke machine method that feeds smoke into the intake, and the smoke comes out at the leak.
A dirty or bad MAF (Mass Air Flow) sensor can cause a P0171 Code.
The onboard computer (ECM) uses the MAF sensor to know how much air has gone into the engine.
If the sensor is reporting bad data, the air ratio will be thrown off.
The upstream Sensor 1 is what reports that there is an air/fuel ratio problem.
While it reports the issue, it does not necessarily mean it is bad, as other failed components can cause the problem.
If the upstream Sensor 1 fails, though, it may be sending out bad data and causing the code.
It can be tested to see if it is having an issue.
A bad fuel injector on Bank 1 can cause a P0171 Code.
One or more injectors may be clogged or have stopped working on Bank 1 side of the engine.
Be sure to check everything else first and do a fuel pressure test, as a fuel injector would be the hardest to replace.