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Ross, Diagnostic and repair technician
Category: Car
Satisfied Customers: 1180
Experience:  Licensed diagnostic and repair technician
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What is the usual cause of fault code P0172

Resolved Question:

what is the usual cause of fault code P0172
Submitted: 2 years ago.
Category: Car
Expert:  Ross replied 2 years ago.
Hi I'm Ross, thanks for trusting me to help you today. I am a diagnostic and repair technician and I look forward to working with you.P0172 is referring to the fuel system being too rich. This is usually caused by a faulty O2 sensor, these are a relatively common failure which will cause an incorrect reading which leads of running rich however there are a few other causes which can be ruled out before replacing an O2 sensor....Condition of the intake air filter, if this is excessively blocked it will cause over fueling.EGR System malfunction - this usually goes hand in hand with EGR system fault codes so is less likelyFaulty fuel pressure regulator, I would recommend a fuel pressure test to ensure the regulator is operating correctlyA leaking fuel injector - again often causes other fault codes but not always so a faulty injector is a possibility if other causes are ruled out. I hope I’ve provided the information you were seeking. If you need more help, please use the reply tab to continue our conversation. If you do not require further assistance, kindly rate my service. Thank you, Ross.
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Customer: replied 2 years ago.

Thanks Ross I shall go and play! The little beast passed an mot cat test after oxygen sensors were replaced! just lights EML light on, and hesitate a little, after 8-20miles.