Isuzu N 2008 Series Workshop Manual page 327

1A-324 Engine Control System (4JJ1)
Checks
Temperature Sensitivity
Electromagnetic Interference (EMI)
and Electrical Noise
Incorrect ECM Programming
Duplicating Failure Conditions
• 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.
• If none of the previous tests are successful, attempt to duplicate and/ or capture the
failure conditions.
• Freeze Frame/ Failure Records data, where applicable, contains the conditions that
were present when the DTC set.
- Review and record Freeze Frame/ Failure Records data.
- Operate the vehicle under the same conditions that were noted in Freeze
Frame/ Failure Records data, as closely as possible. The vehicle must also be
operating within the Conditions for Running the DTC. Refer to Conditions for
Running the DTC in the supporting text of the DTC being diagnosed.
• An alternate method is to drive the vehicle with the DMM connected to a suspected
circuit. An abnormal reading on the DMM when the problem occurs, may help you
locate the problem.
Action