If your 5.7L HEMI Ram cranks but will not start, loses fuel pressure, or has a fuel gauge that reads wrong, the fuel pump circuit is one of the first things to understand. In this guide we redrew the factory diagrams clean and clear so you can follow the wires from the relay, out to the pump in the tank, and back to the computer. Everything below is the fuel pump circuit only, with the unrelated wiring stripped out so it is easy to read.
2003 Dodge Ram 1500 5.7L Fuel Pump Circuit
The 2003 Ram 1500 uses a returnless setup. The fuel pump lives inside the tank as part of a module that also holds the fuel level sender and a filter sock. A fuel pump relay inside the Integrated Power Module feeds battery power to the pump, and the Powertrain Control Module (PCM) decides when that relay turns on. Here is the whole thing on one page, from the relay down to the pump, its grounds, and the signal wires back to the PCM.
Combined fuel pump module circuit for a 2003 Dodge Ram 5.7L showing the fuel pump relay, the DK GRN/WHT feed to the pump module, the black ground path to G103 and G104, and the level sender wires to the PCM.
2003 Dodge Ram 1500 5.7L Fuel Pump Relay and Fuse Location
2003 Dodge Ram 1500 5.7L Fuel Pump Fuel Pump Pins
- Cavity 1: Z211, black wire. This is the pump ground.
- Cavity 2: K4, black with light blue tracer. This is the sensor ground for the fuel level sender.
- Cavity 3: G8, light blue with black tracer. This is the fuel level sensor signal that drives your gas gauge.
- Cavity 4: A64, dark green with white tracer. This is the pump feed coming from the relay.
The pump module plugs into a light gray 4-way connector. Knowing which cavity is which saves you a lot of guessing when you are probing at the tank. Latch faces up, and the cavities read 4, 3, 2, 1 from left to right on the harness side.
If you have power on cavity 4 with the key in Run and a good ground on cavity 1, but the pump is dead, the pump itself is the suspect. No power on cavity 4 sends you back up the circuit toward the relay.
2003 Dodge Ram 1500 5.7L Fuel Pump Relay Pins
- Terminal 30: battery power, hot at all times through Fuse 17.
- Terminal 85: coil power, hot in Run and Start.
- Terminal 86: coil control. The PCM grounds this to switch the relay on, through circuit K31 (brown wire).
- Terminal 87: the output that feeds the pump on circuit A64 (dark green with white tracer).
- Terminal 87A: not used on this circuit.
The fuel pump relay is a standard ISO style relay with five terminals. Think of it as a heavy duty switch. A small control current runs the coil, and that pulls the big contact closed so battery power can reach the pump.
You can bench test the relay quickly. Jump terminal 86 to battery positive and terminal 85 to ground. The relay should click, and you should then read continuity between terminals 30 and 87. If it does not click or does not pass power, replace it.
How is the Pump Powered and Grounded?
- Power in: battery through Fuse 17 to relay terminal 30, and a Run and Start feed through a PTC device to terminal 85.
- Turning it on: the PCM grounds terminal 86 through circuit K31, the relay closes, and terminal 87 sends power out on circuit A64 to pump module pin 4.
- Pump ground: pump pin 1 on the black wire ties into splice S308, then heads to ground at G103 on non ABS trucks or G104 on ABS trucks.
- Fuel level signal: pin 3 carries circuit G8 back to the PCM for your gas gauge. On the 5.7L this signal wire is 20 gauge, and on the 4.7L it is 18 gauge.
- Sensor ground: pin 2 carries circuit K4 to splice S103.
This is the full controls schematic. It shows the relay inside the Integrated Power Module, the PCM control leg, and the ground and signal paths. Reading it left to right and top to bottom keeps it simple.
Why Will Wont my Fuel Pump Work?
When you turn the key to Run you should hear the pump buzz for a second or two as it builds pressure. No prime is your cue to walk the circuit in order instead of throwing parts at it.
- Check the fuel pump fuse first. It is the easy win.
- Check the relay. Swap it with a matching relay in the box, or bench test it as described above.
- Confirm the PCM is grounding the control wire. No control signal at terminal 86 points upstream to the computer or its wiring, not the pump.
- Probe the pump connector at the tank. Look for power on cavity 4 in Run and a solid ground on cavity 1.
- Do not forget the grounds. A bad connection at G103 or G104, or at splice S308, can cause a weak or dead pump even when everything else looks fine.
2003 Dodge Ram 1500 5.7L Fuel Pump and Relay OEM Part Numbers
Amazon Affiliate Link Fuel Pump Dodge Ram 1500 2003 V8 5.7L, Gas, with 26 Gallon Tank
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Amazon Affiliate Link Fuel Pump Dodge Ram 1500 2003 5.7L with 35 Gallon Tank
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Amazon Affiliate Link Mopar OEM Starter Relay: 56049018AB
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Part numbers move around by build, so treat these as a starting point and confirm against your VIN before you buy.
- Fuel pump module for the 5.7L with the 26 gallon tank: Mopar 05086278AA, AB, AC, or AD. The larger 35 gallon tank and the other engines use different numbers, so verify tank size and engine.
- Fuel pump relay: Mopar micro relay 56049018AB, made by Tyco, cross referenced as 72472M. This is the common ISO relay used in several slots of the power module, so match the Fuel Pump position on the box lid diagram.
Summary
The 2003 Ram 5.7L fuel pump story is short once the diagram is understood. Battery power waits at relay terminal 30, the PCM grounds terminal 86 to close the relay, and terminal 87 feeds the pump on the dark green with white wire. The pump grounds through S308 to G103 or G104, and the level sender reports back to the PCM on the light blue with black wire. If you have no prime, work the circuit in order: fuse, relay, control signal, then power and ground at the tank. Always disconnect the negative battery cable, relieve the fuel pressure, and work in a well ventilated area away from any spark or flame before you open up fuel lines or drop the tank.