Field Service Bulletin
CNG Fuel Gauge Inaccurate Readings, Calibration Low
Kenworth T680, T880 and Peterbilt 567, 579

ENP-400
May 27, 2015

1. Introduction

Figure 1 Updating ECU firmware and improving the ground reference signal will cure a
“conservatively reading” dashboard fuel gauge. See text for details.
A small number of Kenworth (T680 and T880) and Peterbilt (567 and 579) CNG vehicles with
dashboard fuel gauges are always reading 1/8 too low than what is in the storage cylinders at all
levels. This can be fixed by updating the electronic control unit (ECU) and modifying the OEM
chassis wire harness to obtain a proper ground signal. This “conservative” fuel gauge reading does
not affect vehicle performance, but is an inconvenience.
This document shows how to modify the wiring on a UPS Kenworth T680, but the modification
steps for the other chassis models are similar. The procedure takes less than 30 minutes.
ECU updates can be performed on the vehicle and is documented in ENP-021, “Updating Engine
Control Unit Firmware and Calibration.”
As an alternative, new ECUs with proper programming can be ordered from Agility Fuel Systems
and old ones can be returned. Use the normal return process per the warranty manual, ENP-067.

2. Affected Units
This procedure affects a certain number of Kenworth T680 and T880 as well as Peterbilt 567 and
579 CNG systems. This procedure is covered under the standard warranty.

3. Special Tools, Materials and Required Parts
1.
2.
3.
4.
5.
6.
7.
8.

Agility Fuel Systems CNG Pressure Simulator, part number 20101007
Weather Pack crimp tool, Delphi part number 12014254
Weather Pack pin removing tool, Delphi part number 12014012
Metri-Pack pin removing tool, Delphi part number 12094429 or 12094430
Adhesive-lined heat shrink tubing for 18 gauge wire
One (1) Weather Pack male terminal, part number 10400030 (Delphi 12089040)
One (1) cavity plug for Metri-Pack connector, part number 10400100 (Delphi 12010300)
One (1) Agility Fuel Systems ECU, Firmware version 5.0, Calibration file PACCAR01.gau,
Agility Fuel Systems part number 20102400

4. Procedure
1. It is not necessary to depressurize the system.
2. Two wire harness connectors are modified in this procedure:

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a. Locate the two-pin connector on the chassis-side wire harness near the center and
behind the back of cab system as shown in Figures 2 and 3. The connector is
labeled “J153, FUEL GAUGE 1” and has one green wire and one blue wire as
shown in Figure 4. The male side of the connector is modified.
b. The second wire harness is a two-pin Weather Pack connector carrying power (red)
and ground (black). The female connector comes from the Agility FMM unit and is
not modified. The male connector comes from the vehicle electrical system and
supplies power to the fuel system. This power connector is located near the fuel
gauge connector.

Figure 2 The two-pin connector/chassis wiring harness for the fuel gauge can be found near
the bottom center of the system cabinet as shown.

Figure 3 The two-pin connector chassis wire harness location.

Figure 4 Locate wire connector “J153, FUEL GAUGE 1”

3. Refer to Figure 5. Remove the green (ground) wire from the chassis connector and
replace it with a cavity plug. The male Metri-Pack contact will be removed and
replaced with a Weather Pack contact in the next step.
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Figure 5 Remove the green (ground) wire from the 2-pin connector and replace it with a
cavity plug (yellow arrow). Remove the male contact (green arrow) on the green wire.

4. Plug the 2-pin chassis harness into the fuel system harness. Remember, the
chassis-side connector now has only one wire as shown in Figure 6.

Figure 6 Plug the 2-pin chassis connector into the fuel system connector. Notice only one
wire is now used at this connection.

5. Remove the Metri-Pack contact and replace it with a male Weather Pack contact as
shown in Figure 7.

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Figure 7 Install a male Weather Pack connector on the green wire as shown.

6. Refer to Figure 8. Locate and disconnect the power and ground connector. Remove
the black (ground) wire pin on the male side of the connector.

Figure 8 The two-pin power (red) and ground (black) connections are located next to
the fuel gauge wire harness.

7. Cut the black wire about an inch from the connector and use adhesive-lined heat
shrink tubing to insulate and weatherproof this wire, it will not be used. Apply heat
shrink tubing over the wire, then pinch the tubing closed while the adhesive is still
hot. See Figure 9.

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Figure 9 Remove the black wire from the male side of the connector. The black wire will not
be used. The green wire removed in steps 3, 4 and 5 will replace the black wire as shown by
the green arrow.

8. Insert the green wire removed from fuel gauge connector into the location
previously occupied by the black wire as shown in Figure 10.

Figure 10 The green wire from the fuel gauge connector is inserted into the power
connector.

9. Re-connect the power and ground connections. The wire harness connector ends
should look like Figure 11.

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Weather Pack connector, power

Metri-Pack connector, fuel gauge
Figure 11 The completed wire harness modifications should look like this.

10. Next, the ECU must be either re-flashed (re-programmed) or replaced with an
updated ECU with the new calibration file (PACCAR01.gau). Refer to Service
Bulletin ENP-021, “Updating Engine Control Unit Firmware and Calibration” for
details, or return the ECU to Agility Fuel Systems Product Support Group (PSG) for
an exchange using the RMA process.
a. Contact Product Support Group (PSG) to order the new ECUs needed for
your fleet.
b. Remove and tag the old ECU with your RMA or vehicle VIN.
c. When the upgrade is completed, return the old ECU to Agility as mentioned
in Section 6.

5. Testing
1. Use the Agility Fuel Systems CNG Pressure Simulator, part number 20101007 to
verify proper gauge operation.
a. Plug the pressure simulator into the fuel system ECU.
b. Test the gauge function by varying the simulator control lever. Sweep
through Empty, Half and Full.
2. Turn on vehicle accessory systems such as the air conditioner, heater/defroster and
rev the engine to see if these conditions cause inaccurate readings.
3. The pressure gauge should correspond to the dashboard fuel gauge as follows:
Dash Fuel Gauge
Reading
Empty
1/4
1/2
3/4
Full

Gas Pressure Gauge
PSI
500
1200
2000
2800
3600

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4. When gauge operation is verified, finalize wire harness routing and clipping and the
vehicle can be returned to service.

6. Warranty Information
1. The standard Agility Fuel Systems warranty applies.
2. Standard repair time (SRT) for this procedure is 0.5 hours.
3. If you are going to return the ECU, rather than re-programming it, use the CRN
procedure in the Warranty Manual, ENP-067, Section 3.6:
a. All removed components must be identified with the CRN.
b. The servicing dealer will have 15 days to return the defective part to Agility.
The package and label containing the returned part(s) must be clearly
marked with the CRN. Return parts may be shipped UPS collect to:
Agility Fuel Systems
Attn: Warranty Processing – CRN ____________
1815 Carnegie Ave
Santa Ana, CA 92705 USA
c. If requested parts are not returned to Agility per the above listed guidelines,
the dealer/service facility will be charged back for all parts contained within
each claim or shipped to the dealer by Agility.
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.

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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

E. Sikes

5/27/15

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