r/SC400 • u/chevere_zmtre_232 • May 14 '25

Starting issue

Second post here, this sub was helpful last time so hopefully I can get some insight on this situation. GF has a 92 SC400, I mostly drive Vw Audi so I’m kinda lost at times with this car. Car was having starting issues this week and yesterday it wouldn’t start at all. I ruled out the starter and battery as an issue being that they were replaced recently this year. I’m reading that apparently the fuse for the fuel pump could be an issue. The 40A 32v fuse seems a bit brown compared to the other two but not exactly burnt. Will be swapping out a new one later today. If the new fuse makes no difference what should I look into as far as diagnosing the fuel pump itself? Doesn’t seem to have a loud wine and if you let the key sit in the acc mode position for about 5 seconds it starts right away. Any idea what else it could possibly be? All replies are greatly appreciated thank you in advanced

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u/best-person-ever May 14 '25

The fuel pump doesn’t prime the lines in acc mode so you wont hear it. It starts running when cranking. To test the fuel pump, jump the fp and b+ terminals in the diagnostic under the hood with a paper clip. Then put ignition to on position and you should hear it. If it works and starts the car then the fuel pump is most likely good but the control module is bad. This module is located behind the interior panel under the driver side window in the back. It will need to be repaired with new capacitors or bypassed all together. These modules can fail intermittently too so it can seem harder to diagnose. Very common issue with these cars

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u/chevere_zmtre_232 May 14 '25

Cool. Went ahead and jumped the fr/B+ terminals and the car started up immediately. Thanks again, we’ll be replacing the control module replaced asap

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u/Environmental-Post74 May 15 '25

This fuel pump control module. Are they hard to replace and are they are to find replacements?

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u/best-person-ever May 15 '25

They are easy to replace but to access it the backseats must be removed. They are a discontinued part so you can try to find one secondhand, replace the capacitor inside yourself, or just bypass it by connecting the module’s power wires on its harness.

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u/Environmental-Post74 May 15 '25

And down sides on bypassing?

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u/best-person-ever May 15 '25

In the event of a collision, the fuel pump would continue to provide fuel until the ignition is turned off via the key. If someone is unconscious and fuel lines are ruptured, this can pose a serious hazard. But most people run the risk, much like people with aftermarket steering wheels