SB-10054660-1491

No.: 12 TS-16REV
December 6, 2013

TO:

Service Locations

FROM:

Technical Service

SUBJECT:

EPA10 Diesel Exhaust Fluid (DEF) Metering Unit Air
Supply Contamination

ISSUE
DEF Metering Units are experiencing rust, oil, and/or debris contamination of the air
supply to the Metering Unit. The contamination can be found at the DEF Metering Unit air
inlet fitting and screen. See item #1 and #2 in the cutaway view of the DEF Metering
Unit, in Figure 1 for the location of the air inlet fitting and screen. The contamination often
results in these codes being logged:
•
•

SPN 3361/FMI 7 – DEF Unit Unable To Clear Restriction
SPN 4335/FMI 7 – DEF Air Pressure Low

Figure 1 – DEF Metering Unit Cutaway View

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12/6/2013

CAUSE
The DEF Metering Unit is NOT the cause of the failure. It is the result of an upstream
failure of the vehicle air supply that causes rust, oil, or debris to be formed in the vehicle
air supply system. See Figure 2 for an example of water in the vehicle air tanks that
caused rust to form and subsequently be passed into the DEF Metering Unit air supply.

Figure 2 – Vehicle Air Tanks With Rust
There should be NO rust, oil, or debris in the DEF air system. Possible causes of the
contamination are as follows:
•
•
•

•
•

Faulty air dryer in the vehicle air system.
Faulty air compressor governor causing the compressor to run longer. A hotter
running compressor will produce hotter air and more water vapor in the air.
Vehicle air system leaks causing the air compressor to run longer than normal. A
hotter running compressor will produce hotter air and more water vapor in the air.
An example of where leaks can be found is the signal line between the primary
tank and governor, especially at the quick-connect fittings.
Plugged air filter.
Plugged air inlet hose from the air filter to the air compressor.

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12/6/2013

Incorrect vehicle air system specification. Some vehicles with high air system
volume requirements have single-cylinder air compressors instead of the more
appropriate twin-cylinder air compressor. This may also impact vehicle air dryer
specifications.
Operator error with failure to drain the water from the vehicle air system on a
daily basis as noted in the Operators Manual.

REQUIRED ACTION
There should be NO rust, oil, or debris in the DEF Metering Unit air system. If
contamination is found, the source must be located and corrected. All DEF air system
components must be inspected and cleaned or replaced. Start the inspection at the air
tanks, then the Pressure Limiting Unit (PLU), then the DEF Pump, and then to the DEF
Metering Unit. Contaminated DEF air supply lines generally can be cleaned.
Contaminated DEF air system components such as the Pressure Limiting Unit ( PLU) and
DEF pump Pneumatic Switching Valve (PSV) air inlet screen can be replaced. The DEF
Metering Unit can be taken apart and the contaminated parts replaced and the air
channel flushed. On DD13 engines, you must also check the air supply to the enginemounted wastegate solenoid for the turbocharger wastegate.

REQUIRED MATERIAL
See Table 1 for a list of commonly needed parts. These part numbers are current as of
November 2013, and are subject to change without notice.
Part Number

Quantity

A0001400594

1

A0001404539

1

A0001420019
A0001400594
WAB975 009 002 0
WAB975 009 101 0

1
1
1
1

Description
DEF Metering Unit Air Inlet Screen – Use only when there
is no contamination in the Diffuser Heater
Diffuser Heater Service Kit – Includes Air Inlet Screen,
Diffuser Heater, and Diffuser Heater O-rings
Pneumatic switching valve
DEF Pump Screen Air Inlet
PLU (Chassis OEM part, Positive Battery Disconnect)
PLU (Chassis OEM part, Negative Battery Disconnect)

Table 1 – DEF Metering Unit Air Supply Parts
REPAIR PROCEDURE
Follow all applicable service procedures in the appropriate service manual.
Troubleshooting information can be found in the EPA07/10 DDEC VI/10 Electronics and
Troubleshooting Manual (DDC-SVC-MAN-0084). Repair information on the DEF system
components can be found in the EPA07/10 Exhaust – EGR – ATS Manual (DDC-SVCMAN-0083).

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12/6/2013

WARRANTY CLAIM PROCESS
The DEF Metering Unit is NOT the cause of this failure and should never be used as the
Primary Failed Part (PFP) on a warranty claim.
If the cause of the air system contamination is chassis-related and the component is
within the guidelines of that product, a warranty claim may be filed to the appropriate
chassis OEM. Note that the air tanks, air lines, air compressor governor, and air
system dryer are chassis OEM parts.
If the cause of the air system contamination is due to operator error (failure to drain the
air tanks), the failure is not warrantable.
CONTACT INFORMATION
Please contact the Detroit™ Diesel Customer Support Center at 800-445-1980 or
email [email protected] if you have any questions.