01 03-19

1

01 03-19

SUBJECT

DATE

SPN 2631/FMI 1 Low Air Flow

January 2019

Additions, Revisions, or Updates
Publication Number / Title
DDC-SVC-MAN-0191

Platform

Section Title

Change

GHG17 DD
Platform

SPN 2631/FMI 1 (MCM)
(GHG17)

Step was added to check the air filter and step was changed to link
to symptom diagnostics for oil in the turbocharger.

DiagnosticLink users: Please update the troubleshooting guides in DiagnosticLink with this newest version. To update the
tool troubleshooting guide, open DiagnosticLink and from the Help – Troubleshooting Guides menu, select the appropriate
troubleshooting manual, then click Update.

All information subject to change without notice.

01 03-19

Copyright © 2019 DETROIT DIESEL CORPORATION

3

2 SPN 2631/FMI 1 - GHG17

2

SPN 2631/FMI 1 - GHG17

Low Air Flow
Table 1.
SPN 2631/FMI 1
Description

This Fault Code Sets When the Engine is in Smoke Mode Control for an Excess Amount
of Time Due to Inadequate Clean Airflow into the Engine

Monitored Parameter

Smoke Mode Operation

Typical Enabling Conditions

General Enabling Condition: Engine is in Smoke Mode
Specific Enabling Conditions: See Table Below
Engine Parameter

Min

Engine Coolant Outlet Temperature

65°C (149°F)

Barometric Pressure (mbar)

755

Ambient Temperature

-8°C (18°F)

Monitor Sequence

None

Max

Execution Frequency

Continuous When Enabling Conditions Met

Typical Duration

13 Seconds

Dash Lamps

MIL, CEL

Engine Reaction

Derate 25%

Verification

Once Engine is at Standard Operating Temperature, Operate Engine on Highway, Coast
for 30 Seconds and then Snap Throttle and Keep Throttle at 100% for a Minimum of 15
Seconds.

Check as follows:
1.
2.
3.
4.

5.

6.

7.

8.

9.

4

Shut off the engine, apply the parking brake, chock the wheels, and perform any other applicable safety steps.
Connect DiagnosticLink ®.
Turn the ignition ON (key ON, engine OFF).
Is the vehicle equipped with a DD16 engine?
a. Yes; Go to step 5.
b. No; Go to step 6.
Check for multiple fault codes. Are there any ITV fault codes present?
a. Yes; diagnose the other fault codes first.
b. No; Go to step 6.
Remove and inspect the air filter. Is the air filter excessively dirty or restricted?
a. Yes; replace the air filter. Refer to OEM guidelines. Verify repair.
b. No; Go to step 7.
Compare the barometric pressure reading in the MCM to the local barometric pressure. Is the barometric pressure
reading in the MCM within 6 kPa (1 psi) of the local barometric pressure?
a. Yes; Go to step 8.
b. No; Replace the MCM.
Compare the intake manifold pressure sensor reading to the barometric pressure reading. Is the intake manifold
pressure sensor reading within 10.3 kPa (1.5 psi) of the barometric pressure reading?
a. Yes; Go to step 10.
b. No; Go to step 9.
Disconnect and inspect the intake manifold pressure sensor electrical connector. Is there any damage or corrosion
present?
a. Yes; repair the connector as necessary.
b. No; replace the intake manifold pressure sensor.

All information subject to change without notice.

Copyright © 2019 DETROIT DIESEL CORPORATION

01 03-19

01 03-19
10. Monitor the EGR Delta Pressure sensor voltage. Is the voltage between 0.55 and 0.83 volts?
a. Yes; Go to step 17.
b. No; Go to step 11.
11. Turn the ignition OFF.
12. Disconnect and inspect the EGR Delta Pressure sensor electrical connector. Is there any damage, corrosion or fretting
present?
a. Yes; replace the EGR Delta Pressure sensor and the pigtail. Verify repair.
b. No; Go to step 13.
13. Remove EGR Delta Pressure sensor from the mounting pad.
14. Reconnect the EGR Delta Pressure sensor electrical connector while the sensor is still removed.
15. Turn the ignition ON (key ON, engine OFF).
16. Monitor the EGR Delta Pressure sensor voltage again. Is the voltage between 0.55 and 0.83 volts?
a. Yes; clean the EGR Delta Pressure ports.
b. No; replace the EGR Delta Pressure sensor.
17. Monitor the Diesel Oxidation Catalyst (DOC) inlet pressure sensor voltage. Is the voltage between 0.44 and 0.56
volts?
a. Yes; Go to step 18.
b. No; replace the DOC inlet pressure sensor.
For 1-Box™, Refer to section "Removal of the Diesel Oxidation Catalyst Inlet Pressure Sensor". Verify repair.
For Two-Box option (2V2), Refer to section "Removal of the Diesel Oxidation Catalyst Inlet Pressure
Sensor".Verify repair.
18. Disconnect and inspect the turbocharger inlet elbow and outlet pipe. Are there signs of oil residue, fluid contamination
or debris?
a. Yes; Go to step 19.
b. No; Go to step 20.
19. Has oil contaminated the Aftertreatment Device (ATD)?
a. Yes; Refer to section "Oil Contamination" and Refer to section "Symptom Diagnostics - Oil Present at the
Turbocharger Compressor Housing". Verify repair.
b. No; Refer to section "Symptom Diagnostics - Oil Present at the Turbocharger Compressor Housing". Verify
repair.
20. Remove and inspect the EGR delivery pipe, crossover pipe and hot pipe. Are there any restrictions present?
a. Yes; clean the EGR system components and reinstall the components.
b. No; reinstall the components. Go to step 21.
21. Disconnect and inspect the DOC inlet pressure sensor hose and sensor. Are there any restrictions present?
a. Yes; clean or replace the hose and sensor as necessary.
b. No; Go to step 22.
WARNING: HOT EXHAUST
During parked regeneration the exhaust gases will be extremely HOT and could cause a fire if
directed at combustible materials. The vehicle must be parked outside.
22. Perform a parked regeneration. Obtain a Regeneration log file and monitor the DOC inlet and DPF outlet pressures.
Refer to section "Performing a Parked Regeneration - GHG17". Does the DOC inlet pressure ever go to zero during
the regeneration?
a. Yes; replace the DOC Inlet Pressure sensor.
For 1-Box™, Refer to section "Removal of the Diesel Oxidation Catalyst Inlet Pressure Sensor".
For Two-Box option (2V2), Refer to section "Removal of the Diesel Oxidation Catalyst Inlet Pressure Sensor".
b. No; Go to step 23.
23. Does the DOC inlet pressure decrease during the regeneration?
a. Yes; the DOC was plugged during the time the code logged causing a restriction. Clear the code and release the
vehicle.

All information subject to change without notice.

01 03-19

Copyright © 2019 DETROIT DIESEL CORPORATION

5

2 SPN 2631/FMI 1 - GHG17
b. No; the DOC is plugged. Perform a DOC Face Plug Cleaning service routine or use the air cleaning procedure.
Refer to section "GHG17 Diesel Oxidation Catalyst Face Cleaning" and Refer to section "Diesel Oxidation
Catalyst Air Cleaning". Verify repairs.

6

All information subject to change without notice.

Copyright © 2019 DETROIT DIESEL CORPORATION

01 03-19