Real Fix: Where there's Smoke ...

July 1, 2017

Smoke machines are valuable tools in diagnosing EVAP system problems. This is what one technician and Mitchell  1 SureTrack community member showed after fixing a 2007 Hyundai Santa Fe GLS 2.7 that came into his shop. Let’s take a look at how he did it with this SureTrack Real Fix.

The Diagnosis

The technician’s first move was to connect the scan tool. Finding the code P2422, EVAP Emission System – Vent Valve Stuck Close, he hooked up a smoke machine to the EVAP system. He induced smoke into the system and found smoke was leaking from the EVAP vent valve, indicating an open vent valve.

To further test, he commanded the EVAP vent solenoid closed with the scanner. As expected, the smoke stopped flowing from the EVAP valve. Again using the smoke machine, he did an EVAP pressure check, which showed the ability to hold pressure.  Using the scan tool, the technician monitored live data and found the EVAP fuel tank pressure sensor signal parameter was above the specified range of 1.4 to 1.6 volts, meaning there is a vacuum in the tank.

He then removed the gas cap only to find that the EVAP parameter would not return to its necessary range. Continuing, the technician inspected and wiggled the pressure sensor wiring harness. The parameter still did not change—still no circuit faults. The tech back-probed the fuel tank pressure sensor signal circuit and watched the sensor signal on a lab scope. Finally, he used a vacuum pump to apply positive pressure to the fuel tank pressure sensor, but the signal did not respond to pressure changes.

The Fix

Because the signal did not change with the adjustments in pressure, it was clear that the fuel tank pressure sensor was faulty. He fixed the problem by replacing the sensor.

Real Fixes from Mitchell 1’s SureTrack® expert information resource are documented issues from actual shop repair orders and community discussions.  Read the Real Fix in the Mitchell 1 ShopConnection Blog.

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