Isuzu 2008MY N Series Workshop Manual page 348

Checks
Temperature Sensitivity
Electromagnetic Interference
(EMI) and Electrical Noise
Incorrect ECM Programming
• An intermittent condition may occur when a component/ connection
reaches normal operating temperature. The condition may occur only when
the component/ connection is cold, or only when the component/
connection is hot.
• Freeze Frame, Failure Records or Snapshot Data may help with this type of
intermittent conditions, where applicable.
• If the intermittent is related to heat, review the data for a relationship with
the following:
- High ambient temperatures.
- Underhood/ engine generated heat.
- Circuit generated heat due to a poor connection, or high electrical load.
- Higher than normal load conditions, towing, etc.
• If the intermittent is related to cold, review the data for the following:
- Low ambient temperatures-In extremely low temperatures, ice may form
in a connection or component. Test for water intrusion.
- The condition only occurs on a cold start.
- The condition goes away when the vehicle warms up.
• Information from the customer may help to determine if the trouble follows a
pattern that is temperature related.
Some electrical components/ circuits are sensitive to EMI or other types of
electrical noise. Inspect the following conditions:
• A misrouted harness that is too close to high voltage/ high current devices
such as injection components, motors, generator etc. These components
may induce electrical noise on a circuit that could interfere with normal
circuit operation.
• Electrical system interference caused by a malfunctioning relay, or the
ECM driven solenoid or switch. These conditions can cause a sharp
electrical surge. Normally, the problem will occur when the malfunctioning
component is operating.
• Improper installation of non-factory or aftermarket add on accessories such
as lights, 2-way radios, amplifiers, electric motors, remote starters, alarm
systems, cell phones, etc. These accessories may lead to an emission
related failure while in use, but do not fail when the accessories are not in
use.
• Test for any open diodes. Some relays may contain a clamping diode.
• Test the generator for a bad rectifier bridge that may be allowing AC noise
into the electrical system.
• There are only a few situations where reprogramming a ECM is
appropriate:
- An ECM from another vehicle is installed.
- Revised software/ calibration files have been released for this vehicle.
Important: DO NOT reprogram the ECM with the SAME software/ calibration
files that are already present in the ECM. This is not an effective repair for any
type of driveability problem.
• Verify that the ECM contains the correct software/ calibration. If incorrect
programming is found, reprogram the ECM with the most current software/
calibration.
Engine Control System (4HK1)
Action
1A-345