This post is partly a cautionary tale, intended to encourage due diligence when diagnosing a driveability problem. A short time ago one of our regular customers brought in their International 4300 with a miss, check engine light, and low power complaint. A short drive confirmed all complaints, and a scan showed an active 456 code. The code descriptor was “Cyl 6 Injector High Side Shorted to Ground or VBAT”. Since the engine had a dead miss while running, I decided to do an injector cutout just to confirm that the rear cylinder was really causing the problem. This was probably redundant with an active code, but I knew I would end up checking harness integrity and didn’t want to get too far along only to discover I had multiple problems. I checked On Command (ISIS) and found the diagnostic process for that code. The manufacturer stated there that code 456 “usually indicates the harness or [injector] coil is shorted to ground”.
This engine was a high-mileage 466E 2004 configuration EGR motor. The ECM/IDM on this engine is on the driver side rear, meaning the doghouse had to come off for access to the IDM connectors. Whenever I pull a doghouse on a 4300/4400, I take off the threshold plates and the passenger bench seat, then roll the floor mat back from around the doghouse. Trying to get the doghouse off with the mat in place will almost certainly tear the mat at the doghouse corners, and it isn’t too much extra work to get it out of the way, once you get used to it.
The IDM (injector driver module) is bolted on top of the ECM (engine control module). It sends high voltage AC power to each injector coil to start and stop injection. High voltage at low amperage is used to provide reliable power for positive injector actuation using small gauge wires.
The harness check is to ohm each conductor between the IDM and the injector in question to check for an open circuit, ohming between pins to check for a crossed connection, then checking each pin for conductance to ground and battery positive. Checking resistance and continuity through the injector coils is the last part of the process. I expected the harness to be open or grounded, maybe under the valve cover but all circuits checked out with nothing open or going to ground or Batt+. Ohming the injector high side coil showed 4.5 ohms against the spec of 1.5 ohms. I would have liked a better indication of a problem, but clearly the injector had to be changed to move forward. An injector change got rid of the active code and the engine now ran normally.
So, at the beginning of the post I stated that this was intended to encourage a complete check for the source of a problem, and it does, but kind of in reverse. I have seen injectors changed on the mere strength of an injector code for that cylinder, without confirming the problem with injector disable or any other tests. You may be able to get away with this sometimes, but sooner or later it will get you in trouble. I know it has me. In the case above, throwing an injector at the problem without the circuit checks would have been the wrong thing to do, even though it fixed the problem. It just happened that this particular injector failure impersonated a problem with the circuit.
Thanks for checking this out
Bruce
This engine was a high-mileage 466E 2004 configuration EGR motor. The ECM/IDM on this engine is on the driver side rear, meaning the doghouse had to come off for access to the IDM connectors. Whenever I pull a doghouse on a 4300/4400, I take off the threshold plates and the passenger bench seat, then roll the floor mat back from around the doghouse. Trying to get the doghouse off with the mat in place will almost certainly tear the mat at the doghouse corners, and it isn’t too much extra work to get it out of the way, once you get used to it.
The IDM (injector driver module) is bolted on top of the ECM (engine control module). It sends high voltage AC power to each injector coil to start and stop injection. High voltage at low amperage is used to provide reliable power for positive injector actuation using small gauge wires.
The harness check is to ohm each conductor between the IDM and the injector in question to check for an open circuit, ohming between pins to check for a crossed connection, then checking each pin for conductance to ground and battery positive. Checking resistance and continuity through the injector coils is the last part of the process. I expected the harness to be open or grounded, maybe under the valve cover but all circuits checked out with nothing open or going to ground or Batt+. Ohming the injector high side coil showed 4.5 ohms against the spec of 1.5 ohms. I would have liked a better indication of a problem, but clearly the injector had to be changed to move forward. An injector change got rid of the active code and the engine now ran normally.
So, at the beginning of the post I stated that this was intended to encourage a complete check for the source of a problem, and it does, but kind of in reverse. I have seen injectors changed on the mere strength of an injector code for that cylinder, without confirming the problem with injector disable or any other tests. You may be able to get away with this sometimes, but sooner or later it will get you in trouble. I know it has me. In the case above, throwing an injector at the problem without the circuit checks would have been the wrong thing to do, even though it fixed the problem. It just happened that this particular injector failure impersonated a problem with the circuit.
Thanks for checking this out
Bruce
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