No power getting to fuel pump.
08-29-2015, 06:57 PM
#1
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2000 clk320 2008 ML350
No power getting to fuel pump.
Changed the fuel pump, fuel filter, cps, fuel pump relay and checked the fuel pump fuse which was ok. It will not start so I checked if there was power getting to the fuel pump and no power. When I probe the fuel pump fuse there is power. Do the wires from the fuel pump fuse go directly to the fuel pump or is it diverted to another location first then to the fuel pump?? Thanks in Advance for any help. David
08-29-2015, 08:40 PM
#2
MBWorld Fanatic!
Not clear what you checked when you said that there is no power getting to the fuel pump. Seems that your focus on checking and/or replacing parts only the high current side of the pump circuitry.
The relay has 4 pins. Two are connected to the relay's switching contacts that close to provide power for the high current circuit that operates the pump. The other two pins are connected to the relay's control coil, that when it sees a control voltage, a low current will flow through the coil and closes the relay contacts, to power the pump.
Have you checked to see if the relay's control coil is being activated?
If not, good way to do this would be to pull the relay and connect a multimeter in series with the relay, set to measure current flow, to the socket connector where the relays coil control would normally plug into.
If the relay coil is not being receiving the control voltage, your trouble shooting needs to look downstream, toward the ECU.
The relay has 4 pins. Two are connected to the relay's switching contacts that close to provide power for the high current circuit that operates the pump. The other two pins are connected to the relay's control coil, that when it sees a control voltage, a low current will flow through the coil and closes the relay contacts, to power the pump.
Have you checked to see if the relay's control coil is being activated?
If not, good way to do this would be to pull the relay and connect a multimeter in series with the relay, set to measure current flow, to the socket connector where the relays coil control would normally plug into.
If the relay coil is not being receiving the control voltage, your trouble shooting needs to look downstream, toward the ECU.
Last edited by Serndipity; 08-30-2015 at 10:09 AM.
08-30-2015, 08:49 AM
#4
MBWorld Fanatic!
The same relay PN is used for the fuel pump as well as the hydraulic pump in the Cabriolets, so since they only cost around $10, I bought a spare to have on hand, if ever needed.
The relay's coil contacts are the 2 that are opposite and positioned parallel to each other and the switching contacts are the 2 that are opposite and positioned at right angles to each other. This will help you identify the socket contacts to connect to.
IMPORTANT: If you perform the test to verify that the relay's input circuitry is operating properly, after you pull the relay, the multimeter and relay coil must be connected in simple series circuit before it is connected to the relay socket. Do not just connect the multimeter with the current setting selected, into the empty relay socket, by itself, as this would connect the control voltage directly to ground (e.g. short circuit) and potentially damage the circuitry that supplies the control voltage.
The resistance of the coil on my spare measured around 85 ohms. By ohms law current flow = voltage / resistance, you should see around 150 milliamps (i.e. mA) of current flow when you check (e.g. set the multimeter to the appropriate measurement range). Off hand I don't know which side of the socket is the + and -. The + connection is the control voltage and the - side is the vehicle ground circuit. On most multimeters, if connected backwards, you should still see current flow, but with a - sign before the number.
While this is the method I would use (e.g. tests relay coil in addition to the ability of the source being able to deliver both the required voltage and current to power the coil), there is a alternative method that simpler.
Just remove the relay and with a multimeter set to measure voltage, attach the meter leads to the socket connections used to control the relay. Because of how volt-meters work , using this method will not damage the the down stream control circuitry.
You should measure about 12 volts. If you see -12 volts, that just means you connected the meter leads backward. In either case, you have verified that the relay socket is getting a control voltage and has a good ground return.
If you do not see any voltage, it means that either the control voltage is not present or the ground return is faulty. If that's the case, you can test which one is faulty by connecting to meters black (-) lead to a known vehicle ground (e.g. negative battery terminal) and the red (+) lead, with the meter still set to measure voltage, to the socket terminal that supplies the control voltage (e.g. which you now know having directly connected both meter leads to the socket). You now can test the ground return by setting the meter to measure ohms and moving the red lead to the socket terminal that connects to ground. You meter should show 0 ohms (or a tiny fraction of).
The relay's coil contacts are the 2 that are opposite and positioned parallel to each other and the switching contacts are the 2 that are opposite and positioned at right angles to each other. This will help you identify the socket contacts to connect to.
IMPORTANT: If you perform the test to verify that the relay's input circuitry is operating properly, after you pull the relay, the multimeter and relay coil must be connected in simple series circuit before it is connected to the relay socket. Do not just connect the multimeter with the current setting selected, into the empty relay socket, by itself, as this would connect the control voltage directly to ground (e.g. short circuit) and potentially damage the circuitry that supplies the control voltage.
The resistance of the coil on my spare measured around 85 ohms. By ohms law current flow = voltage / resistance, you should see around 150 milliamps (i.e. mA) of current flow when you check (e.g. set the multimeter to the appropriate measurement range). Off hand I don't know which side of the socket is the + and -. The + connection is the control voltage and the - side is the vehicle ground circuit. On most multimeters, if connected backwards, you should still see current flow, but with a - sign before the number.
While this is the method I would use (e.g. tests relay coil in addition to the ability of the source being able to deliver both the required voltage and current to power the coil), there is a alternative method that simpler.
Just remove the relay and with a multimeter set to measure voltage, attach the meter leads to the socket connections used to control the relay. Because of how volt-meters work , using this method will not damage the the down stream control circuitry.
You should measure about 12 volts. If you see -12 volts, that just means you connected the meter leads backward. In either case, you have verified that the relay socket is getting a control voltage and has a good ground return.
If you do not see any voltage, it means that either the control voltage is not present or the ground return is faulty. If that's the case, you can test which one is faulty by connecting to meters black (-) lead to a known vehicle ground (e.g. negative battery terminal) and the red (+) lead, with the meter still set to measure voltage, to the socket terminal that supplies the control voltage (e.g. which you now know having directly connected both meter leads to the socket). You now can test the ground return by setting the meter to measure ohms and moving the red lead to the socket terminal that connects to ground. You meter should show 0 ohms (or a tiny fraction of).
Last edited by Serndipity; 08-30-2015 at 11:13 AM.
