Code p0688, truck will not start

2007 DODGE RAM

190,000 MILES • 5.7L • V8 • 4WD • AUTOMATIC

DEREKWHILEY

MEMBER
1 POST
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When I turn my key on, I hear the fuel pump run constantly. It will crank but not start. I replaced the TIPM but no luck. I’ve run it low on gas the last couple of weeks and when I got on the gas pedal, it lost power. I have the code p0688.

May 9, 2022 at 9:45 PM

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KASEKENNY

CAR REPAIR CONTRIBUTOR
18,907 POSTS

If the code, you mentioned above is active then that is where we need to start.

I am attaching the testing below from the manual on this which will be what we need in order to determine what the root cause is.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-use-a-voltmeter

However, if the code is not active then we need to start with checking the fuel pressure. The pump is most likely continuously running because it is not able to build pressure.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Please see the testing below and let me know what questions you have on running through this info.

Thanks

Images (Click to enlarge)

May 10, 2022 at 3:17 PM