7 ELECTRONIC CONTROL SYSTEMS DIAGNOSTICS 523
Tachometer Pin-Point Diagnostics
Figure 497 Tachometer circuit diagram
Key-On Engine-Off Voltage Checks at ECM (Check with key-on engine-off and breakout box connected
[X3 only] to ECM and chassis harness.)
Test Point
Spec Signal Comment
X3–11toX3–7 12V±1.5V
TACH ThesignalispulledupbytheECMwiththekey-on
engine-off.
Connector Checks to Ground at ECM (Check with key-on engine-off and breakout box connected [X3
only] to ECM and chassis harness.)
X3–11 to X3–7
>1kΩ TACH If < 1 kΩ, check for short to ground
either through
the harness or internal ECM. D
isconnect the ECM
from the breakout box and meas
ure to ground
again. If short is still pres
ent, repair harness.
Harness Resistance Checks (Check with key-on engine-off and breakout box connected [X3 only] to
ECM and chassis harness.)
X3–11 to tach
<5Ω TACH Resistance from ECM connector to TACH input –
Optional owner / operator tach.
Key-On Engine-Runnin
g Signal Checks – TACH (Check with key-on engine-off and breakout box
connected [X3 only] t
o ECM an d chassis harness.)
X3–11 to X 3–7 140–700 Hz
Tach signal from the ECM is a frequency that is
engine rpm divided 5. Multiply frequency by 5 to
calculate rpm.
NOTE: The instrument cluster tachometer does not use these outputs. See truck Electrical System
Troubleshooting Guide.
EGES-270-1
Read all safety instructions in the "Safety Information" section of this manual before doing any procedures.
Follow all warnings, cautions, and notes.
© August 2008 Navistar, Inc.
To Next Page
Loading...
Need help?
General