Self-Diagnostics

TM 9-2320-312-24-2

Troubleshooting Section

Engine Snapshot Data

"SHUTDOWN" mode begins by flashing the warning

lamp. This response is similar to the response when

the system is in "DERATE". "SHUTDOWN" mode will

Whenever most diagnostic codes occur, the ECM

eventually shut down the engine if the conditions

records the time in engine hours of the occurrence.

continue for a long enough time and the conditions

Also, the ECM records the operating parameters of

are severe enough. The engine can be restarted as

the engine for 9.6 seconds before the diagnostic

many times as needed after an Engine Monitoring

code and 3.4 seconds after the diagnostic code.

Shutdown. This allows the vehicle to be pulled off

The operating parameters of the engine that are

of the road.

recorded are similar to the operating parameters of

the engine that are displayed in the status screens

of the Electronic Technician. Not all of the status

Other ECM Functions of

screens of the Electronic Technician or parameters

Performance

are recorded. The Engine Snapshot can also be

triggered from the cruise control set/resume switch.

The ECM also provides enhanced control of the

In order to trigger the Engine Snapshot from the

engine for vehicle functions such as exhaust

cruise control set/resume switch, quickly toggle

brake control. Refer to Troubleshooting, "Customer

the switch to the Set position. Then, quickly toggle

Specified Parameters" for supplemental information

the switch to the Resume position. You can also

about the systems that can be monitored by

toggle the cruise control set/resume switch from the

the ECM in order to provide enhanced vehicle

Resume position to the Set position. The Engine

performance, fuel economy and convenience for

Snapshot can also be triggered from the Electronic

the driver.

Technician.

Self-Diagnostics

Effect Of Diagnostic Codes on

Engine Performance

The electronic system has the ability to diagnose

problems. When a problem is detected, a diagnostic

The discussion on engine monitoring mentions that

code is generated and the check engine/diagnostic

the check engine lamp flashes when a specific

lamp may be turned on. In most cases, the code is

condition exists. When the ECM detects the engine

also stored in permanent memory or logged in the

problem, the ECM generates an active diagnostic

ECM.

code. Also, the ECM logs the diagnostic code

in order to indicate the time of the problem's

When diagnostic codes occur, the diagnostic

occurrence. The ECM also logs the number of

codes are called active diagnostic codes. Active

occurrences of the problem. There are two types of

diagnostic codes indicate that a problem of some

diagnostic codes. There are fault codes and event

kind currently exists. Active diagnostic codes

codes.

should always be serviced before any other work is

performed. If a truck is brought in with an active

Diagnostic Fault Codes

code, find the code in the table of contents and

proceed to diagnose the cause.

Diagnostic fault codes are provided in order to

indicate that an electrical problem or an electronic

Diagnostic codes that are stored in memory are

problem has been detected by the ECM. In some

called logged diagnostic codes. Logged diagnostic

cases, the engine performance can be affected

codes do not necessarily indicate that something

when the condition that is causing the code exists.

needs to be repaired. The problem may have been

More frequently, the driver cannot detect any

temporary, or the problem may have been repaired

difference in the engine performance.

since the problem was logged. Logged diagnostic

codes are instead meant to be an indication of

If the check engine lamp is flashing and the driver

probable causes for intermittent problems.

indicates that a performance problem occurs, the

diagnostic code may indicate the cause of the

Diagnostic codes that identify operating conditions

problem. The problem should be corrected.

outside the normal operating range are called

events. Event codes are not typically an indication

If the driver does not indicate a problem with

of an electronic system problem.

the engine performance and a diagnostic code

is logged by the ECM, the situation indicates

Some of the diagnostic codes require passwords to

that the ECM detected an abnormal condition,

be cleared from memory. Diagnostic codes that do

but the abnormal condition did not affect engine

not require passwords to be cleared from memory

performance.

are automatically deleted after 50 hours of engine

operation.