SPN 21 - FMI 0 (Fault Codes: Too many SRS/ missing TRS)
SPN 21 FMI 0
SPN21 FMI0
Flash Code 41 - Too many SRS (Detroit 60 Series)
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| Figure 1.1 - Too many SRS (EEC Information Display) |
Here the STEPS:
1). Connect DETROIT Engine DDEC using Detroit Diesel Diagnostic Link (DDDL v6.46). Read More: How to Connecting DETROIT Engine using Detroit Diesel Diagnostic Link (DDDL).
2). Once connected, open Diagnostics - Fault Codes menu.
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3). Troubleshooting Help - Flash Code 41
DDC Code # (Flashed) = 41
PID = S21
FMI = 0
Fault Description = Too many SRS (missing TRS)
Effect = 1). Engine will shutdown suddenly (when engine is running), or Engine will NOT STARTS (cranking only). 2). Engine will rough (hunting) on high idle (1400 rpm above).
#DESCRIPTION OF FLASH CODE 41
Flash Code 41 indicates that the ECM has detected extra Synchronous Reference Sensor (SRS) pulses, or the ECM has detected missing Timing Reference Sensor (TRS) pulses.
#TROUBLESHOOTING FLASH CODE 41
1). Check for Signal Open
A. Turn ignition OFF.
B. Disconnect engine harness connector at the ECM of the ECM associated with the code.
C. Read resistance between sockets T1 and T2 (S1 and S2) on the engine harness connector.
→If the resistance reading is less than or equal to 200 ohms (Refer to: Check for Short).
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DDC Code # (Flashed) = 41
PID = S21
FMI = 0
Fault Description = Too many SRS (missing TRS)
Effect = 1). Engine will shutdown suddenly (when engine is running), or Engine will NOT STARTS (cranking only). 2). Engine will rough (hunting) on high idle (1400 rpm above).
#DESCRIPTION OF FLASH CODE 41
Flash Code 41 indicates that the ECM has detected extra Synchronous Reference Sensor (SRS) pulses, or the ECM has detected missing Timing Reference Sensor (TRS) pulses.
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| Figure 1.3 - SRS and TRS |
#TROUBLESHOOTING FLASH CODE 41
1). Check for Signal Open
A. Turn ignition OFF.
B. Disconnect engine harness connector at the ECM of the ECM associated with the code.
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| Figure 1.3 - Engine Harness Connector |
→If the resistance reading is less than or equal to 200 ohms (Refer to: Check for Short).
→If the resistance reading is greater than 200 ohms or open (Refer to: Open Timing Reference Sensor Line Check).
2). Check for Short
Perform the following steps to check for a short.
A. Disconnect the TRS/ SRS connector.
B. Measure resistance between sockets T1 and T2 (S1 and S2) on the engine harness connector.
→If the resistance measurement is greater than 10k ohms or open (Refer to: Check Timing Reference Sensor Resistance).
→If the resistance measurement is less than or equal to 10k ohms, a short exists between #110 and #109 or where less than 10k ohms resistance was read, repair the short.
3). Open Timing Reference Sensor Line Check
Perform the following steps to check the open TRS/ SRS line.
A. Disconnect the TRS/ SRS connector.
B. Install a jumper wire between sockets A and B of the TRS/ SRS harness connector.
C. Measure resistance between sockets T1 and T2 (S1 and S2) on the engine harness connector.
→If the resistance measurement is less than or equal to 5 ohms (Refer to: Check Timing Reference Sensor Resistance).
→If the resistance measurement is greater than 5 ohms or open, the signal line #110 or return line #109 is open, repair the open.
4). Check Timing Reference Sensor Resistance
Perform the following steps to check TRS/ SRS resistance.
A. Measure resistance of TRS/ SRS across sensor connector pins A and B.
→If the resistance measurement is greater than 200 ohms (Refer to: Open Timing Reference Line Check).
→If the resistance measurement is less than 100 ohms (Refer to: Check for Short).
→If the resistance measurement is between 100 and 200 ohms (Refer to: Check Timing Reference Sensor / Synchronous Reference Sensor Gap)
5). Check Timing Reference Sensor / Synchronous Reference Sensor Gap
Perform the following steps to check the TRS/ SRS gap.
A. Bar the engine until the TRS/ SRS is over a TRS tooth of the pulse wheel.
B. Check the gap between TRS and the tooth of the pulse wheel (TRS: 0.020 to 0.040 in). A depth micrometer can be used.
→If the gap setting is not correct, adjust the TRS/SRS until the gap setting is correct. If the problem returns, the pulse wheel may be loose or bad or damaged.
6). Check TRS/ SRS Connectors
A. Check terminals at the TRS/ SRS (both the TRS/ SRS and harness side) for damage: bent, corroded, and unseated pins or sockets, or bad contacts.
→If terminals and connectors are damaged, repair them.
→If terminals and connectors are not damaged, replace the TRS/ SRS.
#Additional Information
1. SYNCHRONOUS REFERENCE SENSOR
The Synchronous Reference Sensor (SRS) is an electronic component that is mounted to the rear of the gear case.
The sensor portion of the SRS extends through a hole in the gear case, and is positioned very
near the rear of the bull gear. A bolt, inserted through a hole in the SRS bracket, secures the SRS
assembly to the gear case. The SRS connector is black in color.
The SRS sends a signal to the ECM. This signal is generated by a raised metal pin on the rear
of the bull gear.
The bull gear pin passes by the SRS as the number one piston reaches approximately 45 degrees
before Top-Dead-Center (TDC). This information is used by the ECM to determine number one
piston in the firing order.
2. TIMING REFERENCE SENSOR
The Timing Reference Sensor (TRS) is an electronic component that is mounted to the left side of
the gear case, near the crankshaft centerline.
The sensor portion of the TRS extends through an opening in the gear case, and is positioned near
the teeth of the timing wheel. A bolt, inserted through a hole in the TRS bracket, secures the TRS
assembly to the gear case. The TRS connector is gray in color.
The TRS sends a signal to the ECM. This signal is generated by a series of evenly spaced teeth on
the timing wheel. As the timing wheel rotates with the crankshaft, a tooth passes by the TRS.
These signals are used by the ECM to determine injector solenoid operation times and engine
speed.
2). Check for Short
Perform the following steps to check for a short.
A. Disconnect the TRS/ SRS connector.
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| Figure 1.4 - Engine Harness Connector to Timing Reference Sensor |
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| Figure 1.5 - Engine Harness Connector to Synchronous Reference Sensor |
→If the resistance measurement is greater than 10k ohms or open (Refer to: Check Timing Reference Sensor Resistance).
→If the resistance measurement is less than or equal to 10k ohms, a short exists between #110 and #109 or where less than 10k ohms resistance was read, repair the short.
3). Open Timing Reference Sensor Line Check
Perform the following steps to check the open TRS/ SRS line.
A. Disconnect the TRS/ SRS connector.
B. Install a jumper wire between sockets A and B of the TRS/ SRS harness connector.
C. Measure resistance between sockets T1 and T2 (S1 and S2) on the engine harness connector.
→If the resistance measurement is less than or equal to 5 ohms (Refer to: Check Timing Reference Sensor Resistance).
→If the resistance measurement is greater than 5 ohms or open, the signal line #110 or return line #109 is open, repair the open.
4). Check Timing Reference Sensor Resistance
Perform the following steps to check TRS/ SRS resistance.
A. Measure resistance of TRS/ SRS across sensor connector pins A and B.
→If the resistance measurement is greater than 200 ohms (Refer to: Open Timing Reference Line Check).
→If the resistance measurement is less than 100 ohms (Refer to: Check for Short).
→If the resistance measurement is between 100 and 200 ohms (Refer to: Check Timing Reference Sensor / Synchronous Reference Sensor Gap)
5). Check Timing Reference Sensor / Synchronous Reference Sensor Gap
Perform the following steps to check the TRS/ SRS gap.
A. Bar the engine until the TRS/ SRS is over a TRS tooth of the pulse wheel.
B. Check the gap between TRS and the tooth of the pulse wheel (TRS: 0.020 to 0.040 in). A depth micrometer can be used.
→If the gap setting is not correct, adjust the TRS/SRS until the gap setting is correct. If the problem returns, the pulse wheel may be loose or bad or damaged.
6). Check TRS/ SRS Connectors
A. Check terminals at the TRS/ SRS (both the TRS/ SRS and harness side) for damage: bent, corroded, and unseated pins or sockets, or bad contacts.
→If terminals and connectors are damaged, repair them.
→If terminals and connectors are not damaged, replace the TRS/ SRS.
#Additional Information
1. SYNCHRONOUS REFERENCE SENSOR
The Synchronous Reference Sensor (SRS) is an electronic component that is mounted to the rear of the gear case.
 |
| Figure 2.1 - Synchronous Reference Sensor Location |
near the rear of the bull gear. A bolt, inserted through a hole in the SRS bracket, secures the SRS
assembly to the gear case. The SRS connector is black in color.
The SRS sends a signal to the ECM. This signal is generated by a raised metal pin on the rear
of the bull gear.
 |
| Figure 2.2 - Bull Gear |
before Top-Dead-Center (TDC). This information is used by the ECM to determine number one
piston in the firing order.
2. TIMING REFERENCE SENSOR
The Timing Reference Sensor (TRS) is an electronic component that is mounted to the left side of
the gear case, near the crankshaft centerline.
 |
| Figure 2.3 - Timing Reference Sensor Location |
the teeth of the timing wheel. A bolt, inserted through a hole in the TRS bracket, secures the TRS
assembly to the gear case. The TRS connector is gray in color.
The TRS sends a signal to the ECM. This signal is generated by a series of evenly spaced teeth on
the timing wheel. As the timing wheel rotates with the crankshaft, a tooth passes by the TRS.
These signals are used by the ECM to determine injector solenoid operation times and engine
speed.
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