Last updated: May 15
OBD2 and reading codes
If you don’t have an OBD2 reader you should definitely consider getting one. Even if you are not into DIY, being able to read a code before taking your car to the shop can sometimes save a diagnostic fee or give you confidence if a shop provides a diagnosis that matches up with the code you’ve pulled. OBD2 ports have been required on cars in the US since 1996, Europe since 2004 and Australia/New Zealand since 2006 source.
Anyhow, OBD2 readers are very affordable. I picked mine up for £22 on Amazon.
Here we see the P0171: System too lean code.
System too lean, what does it mean?
It’s a pretty straightforward issue in a sense. The car’s computer is calculating a lean fuel to air ratio. So either the engine is getting too much air or not enough fuel. For my Corsa MK4, it looks at the MAF (Mass Airflow sensor) which measure the amount of air going into the engine, and the O2 sensor (Lambda sensor) bank 1 location which measures the amount of oxygen left unburnt coming out of the engine.
There’s plenty of reasons why you might have a lean system unfortunately. Sensors have gone bad, cracked manifold, slow fuel pump but this age of GM vehicles seems to have a common culprit.
A hunch
After doing a bit of googling I stumbled upon this YouTube video Vauxhall Corsa running issue fixed Fault code P0171. The symptoms sounded the same, an intermittent check engine code, with a code read of P0171. His diagnosis was the Purge valve.
Thankfully it looks like once you remove the purge valve it’s very easy to tell whether there’s an issue. The valve is normally closed and should only open occasionally, allowing petrol vapors from the fuel tank to be burned up in the engine. If you blow in one end and any air leakage occurs at all (in essence the valve is allowing more air into the engine than expected), the valve is busted and needs replacing.
If you’re interested in what a Purge valve does I found a solid write-up on this website: Purge valve: how it works, symptoms, problems, testing.
Below you can see the placement of the purge valve in the engine bay.
Removing
In order to remove the purge valve you have four different things to disconnect. On the right, you have a metal bracket with a pair of screws and an outgoing rubber hose. On the left you have an electrical plug and incoming plastic hose.
Even a stubby screwdriver is too tall for the screws, placing the screwdriver head in a 1/4” drive socket did the trick just fine though.
Once the metal bracket is removed you can pull the rubber tube / purge valve away.
The electrical plug has a slot you can place a flat head screwdriver and then leverage away (in this case left) to release.
There are two clips holding in the incoming hose. I removed the green clip first and then white clip.
Diagnosis
In order to confirm the valve is the issue we can just blow into the incoming tube. Yup, my purge valve was stuck open.
Replacing
Ordering the part was straightforward. You’re looking for Bosch part# 0 280 142 486. OEM number is 55 566 514 (Chevrolet, Opel, Vauxhall). I found this one at autodoc.co.uk
It’s probably worth noting that you’ll need to re-use the metal bracket and rubber L tube. The tube itself was difficult to remove. Pulling on it makes it squeeze tighter, I found that wrapping some string around the plastic side was able to nudge it forward enough to release a little easier.
Success!
With the new valve in place I was able to clear the code and it never came back! Looks like we found the right issue.
