Tachometer Pin-Point Diagnostics - Navistar International DT 466 Diagnostic/Troubleshooting Manual

7 ELECTRONIC CONTROL SYSTEMS DIAGNOSTICS

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
X3–11 to X3–7 12 V ±1.5 V
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 > 1 kΩ
Harness Resistance Checks (Check with key-on engine-off and breakout box connected [X3 only] to
ECM and chassis harness.)
X3–11 to tach < 5 Ω
Key-On Engine-Running Signal Checks – TACH (Check with key-on engine-off and breakout box
connected [X3 only] to ECM and chassis harness.)
X3–11 to X3–7 140–700 Hz
NOTE: The instrument cluster tachometer does not use these outputs.
Troubleshooting Guide.
Read all safety instructions in the "Safety Information" section of this manual before doing any procedures.
Signal Comment
TACH The signal is pulled up by the ECM with the key-on
engine-off.
TACH If < 1 kΩ, check for short to ground either through
the harness or internal ECM. Disconnect the ECM
from the breakout box and measure to ground
again. If short is still present, repair harness.
TACH Resistance from ECM connector to TACH input –
Optional owner / operator tach.
Tach signal from the ECM is a frequency that is
engine rpm divided 5. Multiply frequency by 5 to
calculate rpm.
EGES-270-1
Follow all warnings, cautions, and notes.
© August 2008 Navistar, Inc.
See truck Electrical System
523