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Hello, went to go for a cruise and the C300 won't start. Scanner has two codes. 2081 communication with control unit fuel pump has a malfunction and 0490 the output for the fuel pump has a short circuit to ground. Appears no power to the fuel pump at all. No noise. Checked fuses and swapped the relay in the rear SAM still nothing. Thinking FSCU is dead? Looked at the inside of the FSCU and visually it looks fine no blown caps or anything obvious.
Hello, went to go for a cruise and the C300 won't start. Scanner has two codes. 2081 communication with control unit fuel pump has a malfunction and 0490 the output for the fuel pump has a short circuit to ground.
Appears no power to the fuel pump at all.
No noise. Checked fuses and swapped the relay in the rear SAM still nothing.
Thinking FSCU is dead?
Looked at the inside of the FSCU and visually it looks fine no blown caps or anything obvious.
Preliminary checks done.
Relay and fuses reported ok.
Can you connect DVM at the FSCU to read 12VDC near battery voltage?
This step should validate good power supply including a working (painted) GND source under load.
When going from any of the connections on the four pin connector there is no power present on any single pin to ground. Just to confirm which is the fuel pump relay and fuse?
the relay you can swap with a similar one on the SAM. If that dont change anything you can remove the top cover off the relay and then manally operate the relay and see if that works. if it dont work manually you will know its not getting the right power or you have a bad pump possibly.
Definitely not getting power to the FSCU as it can't be communicated with a scanner. I've got power at both front and rear SAM fuses for the fuel pump. Can't find a definitive answer on which one/Where is the fuel pump relay. It's also totally possible a bad ground. But if I am grounding the pins on the 4 Pin connector at the FSCU, I should have seen voltage on at least one of the pins and I've got nothing.
Looks like the relay is in the front SAM? If so it appears to also run the throttle body. Getting power there and confirmed all three of the smaller relays in the rear and the front ones are good relays. Still no power to the FSCU. I assume I'm looking for 12V somewhere on the 4 Pin connector?
Fuel pump is new Hella unit around 6 months old and has been working fine. Not saying it couldn't be an issue but the scanner can't see the FSCU.
Now this is the same FSCU that was giving low fuel pressure alerts and that was actually a result of corrosion on one of the small 8 Pin connectors on the FSCU. Once that was cleaned up never had the code again. Also this one is not the original. Prior to buying the vehicle someone had replaced this before.
Ok after reviewing the spec sheet it appears that the 4 pins are outputs and the input is the 8 Pin. So I wasn't checking power in the right spot.
Nevertheless found one chip loose on the board. It's one with two legs on one side and one on the other not sure what it does. Ordered a new FSCU hopefully it will bring it to life.
Went through all the fuses again. All are good. Front and rear SAM tests with scanner show all good.
At this point I can only think possible issue with the ME or the Pre-Fuse box. The vehicle only has three wires at the top and there is continuity between all lugs except an unused one at the far back left closest to the battery. I assume I am going to have to pull the whole thing out to test further. It appears there is a fuse from that box that feeds the FSCU unless I am mistaken.
Found the issue. The connector that feeds power to the FSCU is in the rear SAM and it's a blue plug on mine. It was not fully clipped in. She runs smooth as glass again!!!!
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