Skip to content Skip to sidebar Skip to footer

√ Fault Codes: Fuel Pressure Circuit Low (Detroit Diesel Diagnostic Link)

Flash Code 38 - Fuel Pressure Sensor - Input Voltage Low (DETROIT 60 Series)

Figure 1.1 - Fuel Pressure Circuit Low (EEC Display)

Read More:


Fuel pressure sensing is currently only configured for some industrial engines. It is not available
on all series. The fuel pressure sensor used is the same as the oil pressure sensor.

DDC Code # (Flashed) = 38
PID = P94
FMI = 4
Fault Description = Fuel Pressure Sensor (FPS) Low

DESCRIPTION OF FLASH CODE 38
Flash Code 38 indicates that the engine Fuel Pressure Sensor (FPS), see Figure 1.2, input to the
ECM has dropped below 5% (normally < 0.25 volts) of the sensor supply voltage.

This diagnostic condition is typically:
-Open sensor signal circuit
-Open sensor +5 volt supply circuit
-Sensor signal is shorted to sensor return circuit or to ground
-Sensor +5 volt supply is shorted to the sensor return circuit
Figure 1.2 - Fuel Pressure Sensor

TROUBLESHOOTING FLASH CODE 38
1). Multiple Code Check
Perform the following steps to check for multiple codes.
1. Turn vehicle ignition switch ON.
2. Plug the diagnostic data reader (DDR) into the diagnostic data link (DDL).
Read More: How to Connecting DETROIT Engine using Detroit Diagnostic Link (DDDL).
3. Read active codes.
Figure 1.3 - FPS Input Voltage Low (PID P94 - FMI 4) 
-If active code 94/4 and no other codes were logged, refer to "Sensor Check".

2). Sensor Check
Perform the following steps to check the sensor.
1. Turn ignition switch OFF.
2. Disconnect FPS connector and install a jumper wire between sockets B and C of the
FPS harness connector. See Figure 1.4.
3. Turn ignition ON.
4. Read logged codes.
5. If active codes 94/3 or 4 are not logged, start and run the engine until either these active codes display or engine temperature (COOLANT TEMP & OIL on DDR) has been greater than 60 deg C (140 deg F) for more than one minute.
-If active code 94/4 and any other codes are logged, refer to "Check for +5 Volts".
-If active code 94/3 and any other codes except code 94/4 are logged, check to ensure ECM and FPS connectors are wired properly. Refer to "Check Fuel Pressure Sensor Connectors".
Figure 1.4 - Engine Harness Connector to Fuel Pressure Sensor

3). Check Fuel Pressure Sensor Connectors
Perform the following steps to check the FPS connectors.
1. Inspect terminals at the FPS connectors (both the sensor and harness side) for damage: bent, corroded, and unseated pins or sockets.
-If the terminals and connectors are damaged, repair them.
-If the terminals and connectors are not damaged, replace the FPS.

4). Check for +5 Volts
Perform the following steps to check for +5 volts.
1. Turn vehicle ignition OFF.
2. Remove jumper wire.
3. Turn ignition ON.
4. Measure voltage on FPS harness connector, socket C to socket A. See Figure 1.4.
-If the voltage measurement is greater than 6 volts, refer to "Check for Short to Battery +".
-If the voltage measurement is less than 4 volts, refer to "Check for Open +5 Volt Line".
-If the voltage measurement is between 4 and 6 volts, refer to "Check for Signal Open".

5). Check for Signal Open
Perform the following steps to check for signal open.
1. Turn vehicle ignition OFF.
2. Disconnect engine harness connector at the ECM.
3. Install a jumper wire between pins A and B of the FPS harness connector.
4. Measure resistance between sockets M1 and Y2 on the engine harness connector.
-If resistance measurement is less than or equal to 5 ohms refer to "Check for Short to Ground".
-If the resistance measurement is greater than 5 ohms or open, the signal line (#905) or return line (#452) is open. Repair the open.

6). Check ECM Connectors
Perform the following steps to check the ECM connectors.
1. Check terminals at the ECM harness connector (both ECM and harness side) for damage: bent, corroded, and unseated pins or sockets. Check W1, M1 and Y2 terminals at ECM.
-If terminals and connectors are damaged, repair them.
-If terminals and connectors are not damaged, install a test ECM.

7). Check for Open +5 Volt Line
Perform the following steps to check for open +5 volt line.
1. Turn vehicle ignition OFF.
2. Disconnect the engine harness connectors at the ECM.
3. Install a jumper wire between sockets A and C of the FPS harness connector. See Figure 1.4.
4. Measure resistance between sockets W1 and Y2 on the engine harness connector.
-If resistance measurement is less than or equal to 5 ohms, refer to "Check for Short".
-If the resistance measurement is greater than 5 ohms or open, the engine +5 volt line (#416) is open. Repair the open.

8). Check for Short to Battery +
Perform the following steps to check for a short to battery.
1. Remove both fuses to the ECM.
2. Disconnect the vehicle harness and 5-way power connectors at the ECM. See Figure 1.5.
3. Measure resistance between socket W1 on the engine harness connector and socket B3 of the vehicle harness connector, and between W1 and the 5-way power harness sockets A and C.
-If the resistance measurement is greater than 1,000 ohms or open, replace the FPS.
-If the resistance measurement is less than or equal to 1,000 ohms, a short exists between sockets where less than 1,000 ohms was measured. Repair short and reinsert fuses.
Figure 1.5 - ECM Vehicle Harness Connector

9). Check for Short to Ground
Perform the following steps to check for a short to ground.
1. Turn ignition switch OFF.
2. Remove jumper wires.
3. Measure resistance between sockets M1 and Y2 on the engine harness connector. Also measure resistance between socket M1 and a good ground.
-If both resistance measurements are greater than 100 ohms or open, replace the FPS.
-If either resistance measurement is less than or equal to 100 ohms, the signal line (#905) and return line (#452) are shorted together, or the signal line (#905) is shorted to battery ground. Repair short.


Read More:
FREE DETROIT E-Parts Catalog
FREE DETROIT Wiring Diagrams