Field Service Bulletin
Remove and Replace Electronic Control Unit (ECU)

ENP-405
June 17, 2015

1. Introduction
All CNG systems (and many LNG systems) include an Agility Fuel Systems electronic control unit
(ECU) as part of the fuel management module (FMM). There are several versions of the ECU
“black box,” but they all share the same housing, interface connectors and labeling, see Figure 1.
Removing and replacing the ECU is easy, however, access to the ECU inside the FMM housing
may be challenging. Here are some hints to ensure success.

Figure 1 An Agility Fuel Systems ECU. The label, located at the center of the top cover, includes
serial number and software version information.

2. ECU Locations
See Figures 2 and 3. In several CNG system configurations, the FMM components and ECU are
contained inside a chassis box usually located on the driver’s side of the vehicle.

Figure 2 FMM “box unit” mounted on a chassis rail. The arrow points to the ECU in the upper left
corner of the FMM cabinet.

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Figure 3 The ECU is fastened to the top of the FMM chassis box with four bolts as shown.

Refer to Figures 4 and 5. On side mount systems, the ECU is fastened to the fuel system frame at
the approximately 1- or 2-o’clock position inside the FMM end of the cylinder cover. The ECU
location may vary, but should be easy to access by opening the maintenance side door.

Figure 4 The ECU is mounted on the system chassis near the top in side mount configurations, but
this location may vary.

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Figure 5 Typical ECU location in a rail- or side-mount system. The ECU will always be mounted on
the FMM side of the system.

Figures 6 and 7 show an ECU in a back of cab system, accessible behind a door panel and
mounted to a frame member.

Figure 6 The ECU is mounted to a plate attached to the system frame in this back of cab system.

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Figure 7 ECU location in a back of cab system.

3. ECU Wiring Harnesses

Figure 8 Push or press the locking tab to release the 16- and 4-pin wire harnesses from the
ECU. Make sure you pull the connector and not the wires when removing the wire harness
from the ECU.

4. Special Tools, Materials and Required Parts
1. None

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5. Procedure
1. Cabinet Style FMM
a. The FMM cabinet does not have to be removed from the vehicle.
b. Remove the bottom cover to gain access to the FMM components and ECU.
c. Release the wire harness connector latches and un-plug the wire harnesses from the
ECU.
d. Using a long extension bar and socket, remove the four fasteners (screws or bolts)
holding the ECU to the FMM cabinet cover.
2. Side Mount Systems
a. Open the maintenance side door or cover on the FMM side of the system cabinet to gain
access to the FMM components and ECU.
b. Release the wire harness connector latches and un-plug the wire harnesses from the
ECU.
c. Using a long extension bar and socket, remove the four fasteners (screws or bolts)
holding the ECU to the FMM cabinet cover.
3. Back of cab systems
a. Open the fuel system cabinet on the FMM side of the system to gain access to the FMM
components and ECU.
b. Release the wire harness connector latches and un-plug the wire harnesses from the
ECU.
c. Using a long extension bar and socket, remove the four fasteners (screws or bolts)
holding the ECU to the FMM cabinet cover.
4. Reverse the process to install the new ECU into the system.

6. Warranty Information
1. Does not apply. This is a description for any work involving the ECU.
If you have any questions, contact Agility Fuel Systems Product Support at 949-267-7745 or
[email protected].
Agility Fuel Systems Product Support Group, 1815 Carnegie Ave., Santa Ana, CA 92705 USA
Proprietary Statement
The information provided within this document is proprietary and confidential. All prior versions,
including updates and revisions forwarded separately, are proprietary. The information provided by
Agility Fuel Systems to its customers and clients is solely for the use of those customers and
clients. No portion of this manual may be reproduced or distributed without express written consent
of Agility Fuel Systems. Agility Fuel Systems reserves the right to utilize the intellectual property
contained within this publication as content for any other publication produced by Agility Fuel
Systems.
Trademark Notice
Agility Fuel Systems® is a registered trademark of Agility Fuel Systems. Drop-N-Go™ is a
trademark of Agility Fuel Systems. Trademarks of other manufacturers are the property of their
respective companies.
Revision

Description

Author

Approved By

Date

--

Initial Release

W. Yoshida

A. Bhakta

6/17/15

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