All about error P0171: what it means, what is dangerous, how to fix it
A lean mixture error can not only reduce engine performance, but also cause significant damage.
Error P0171 “lean mixture” can occur for a number of reasons, but you need to remember the main thing: you can’t delay the solution. In addition to unpleasant symptoms (jerks, dips, etc.), the consequences can be detonation – one of the most dangerous phenomena in the engine operating cycle.
Lean mixture: what is it
The concept implies a violation of the stoichiometric composition of the mixture towards depletion. In simple terms, the set ratio of gasoline and air is knocked down: there is less gasoline than necessary. Or the second option: the gasoline supply is normal, but there is more air in the cylinder. In both cases, the fuel-air mixture becomes depleted.
The opposite example: if there was more fuel, or there was a lack of air, then the opposite process would occur – enrichment.
Causes of error P0171 (lean mixture)
As we have already found out, a lean mixture is formed according to two scenarios: not enough fuel or too much air. Let’s list the probable reasons for both.
Low on fuel
Fuel pressure problem. The main “suspects” are the fuel pump and the pressure regulator on the fuel rail. Moreover, the pump itself is often fine, and the interruptions are caused by a heavily contaminated coarse filter mesh in the gas tank or a clogged fuel filter.
Problem with the injectors. They can either fail mechanically or become clogged with dirt or abrasives.
Lots of air
Leaks in the intake tract. Commonly known as air leaks.
Problems with the throttle valve, when more air is passed than required for a given operating mode.
A failure in the valve timing mechanism, resulting in the working cycles not occurring on time.
Combined causes
This includes sensors that affect mixture formation. In particular, the causes of the P0171 error may be the throttle position sensor (TPS), the oxygen sensor (lambda probe), the mass air flow sensor (MAF) and other components involved in the formation of the proportion of fuel with oxygen.
An exotic option is a malfunction of the control unit, when the fuel may be incorrectly dosed (overflow) even with fully functional components of the fuel system and sensors. But such a scenario, frankly speaking, is extremely rare in practice. Of course, with the exception of cases when the problems did not begin after deliberate interference with the electronics.
Signs of a lean mixture
In addition to the Check Engine on the dashboard, typical symptoms of fuel shortage will be relevant with a lean mixture. These are dips and jerks during acceleration, lack of traction, a “cottony” gas pedal in certain modes, etc.
It is worth noting that in the presence of error P0171, jerks are often not a consequence of a lack of fuel, but the result of an emergency mode of operation of the control unit.
Why is a lean mixture dangerous?
As we mentioned above, the main danger of leanness is the risk of detonation. We discussed this phenomenon in detail in a separate article . If a harmful process is detected, the control unit, in order to save the engine, changes the ignition algorithm, injection and boost control, if any.
However, even the most sensitive and agile electronics act after the detonation has already occurred. Therefore, prolonged ignoring of the P0171 error is fraught with serious engine damage. If you still need to move, then until the problem is fixed, you should avoid working with high loads and at high speeds.
Error P0171 (lean mixture): what to do
Troubleshooting, as always, depends on proper diagnostics. Above, we found out that a lean mixture can be a consequence of a variety of breakdowns. Accordingly, the list of “candidates” for replacement may include elements of the fuel system, intake tract and control sensors.
In fact, the causes of the P0171 error are usually easily diagnosed with a simple Chinese OBD scanner. The device is quite inexpensive, is presented in a huge variety in online stores, and control is possible even from a smartphone and is available to any beginner.
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