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Old 07-24-2011, 08:07 AM
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ECM Harness Protecctor Removal, 2001 Altima GXE 2.4L

On a 2001 Nissan Altima GXE 2.4L vehicle, the factory service manual frequently indicates that measurements be made from the ECM harness connector to other points. The ECM harness side terminals are accessible only if the harness protector is removed.

Can the harness protector be removed without turning out the screw which appears to back off the ECM connector harness first? Turning the hex screw in the the middle appears to begin disengaging the harness side connector from the ECM side. I am guessing that turning the hex screw all the way out will separate the ECM harness connector from the ECM. Although the instructions do not say it ahead of time, it sounds as if the protector can be removed to make measurements from the wire side of the harness possible but it seems that the entire harness side must first be separated to do so.

The "Trouble Diagnosis" page, EC-98, does not explicitly state it but other documents indicate that the negative battery cable should be removed prior to separation of the ECM harness connector from the ECM with no apparent loss of stored memory.

I need to get access to pin 103 on the ECM harness side connector and would like to remove the harness protector without disconnecting the entire connector but that may not be possible. The way the harness protector is snapped onto the harness side of the ECM connector is not obvious to me and the instructions do not say anything about turning the hex screw out to remove the harness protector which is snapped on by some tricky means.

Any advice on this operation would be helpful since I do not relish the thought of removing and replacing the ECM connector if it is not absolutely necessary with the prospect of pin damage/bent pins/slipped connectors, etc.

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Old 07-24-2011, 08:54 AM
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Quote:
Originally Posted by awbazar
On a 2001 Nissan Altima GXE 2.4L vehicle, the factory service manual frequently indicates that measurements be made from the ECM harness connector to other points. The ECM harness side terminals are accessible only if the harness protector is removed.




If you are testing with a DVOM on the Ohms setting then I would have to say they want you to disconnect the ecm from the harness and test in that fashion.
Unhooking the battery will not erase trouble codes on a 2001
If the manual suggests that you need to check voltages on a specific circuit, then you will need to uncover the back of the connector and backprobe the circuit in question. If so study the cover for a bit. I know it is confusing(believe me I know) so dont rush and break some plastic. you'll figure it out.It would be easier with the connector unhooked from the PCM/ECM as you will be able to get a closer look. Dont worry abot pins backing out, when you look at the connector, you will see a colored piece that slides in from the front side(ecm side) of the connector that is actually a lock to retain the wires and reinforce another lock inside the connector.
When replacing any wire in the connector the primary lock (colored piece)needs to be removed and the release inside the connector has to be pulled back (very tedious) for any wire to be relesaed from the connector.
If you are checking any circuit for a voltage while the key is on or engine running BE SURE you have the correct wire/terminal and use a DVOM with at least 1 megohms internal resistance, 10 megohms is actually recommended now.
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Old 07-24-2011, 10:31 AM
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ECM Harness Protector Removal

Hello Latech,
Thank you for the fast response. From what you said, it sounds as if the right forces on the plastic harness protector will pop it off without messing at all with the center hex nut which would remove the harness side connector completely if fully turned out.

There are 4 slots in the harness protector. Is the insertion of a screwdriver or nonconductive blade like a popsicle stick or the like, needed to release catches?

Your comments on the DVOM are well stated and that is what I am using. I recognized the need for operating voltage measurements to be taken with the ECM connector connected and was leery of taking continuity measurement from the ECM connector harness side elsewhere if it were plugged into the ECM due to the voltages from the meter itself.

I got to this point working to eliminate a P1400, EGRC solenoid valve circuit failure. My last prospect was continuity of the wire to the ECM to pin 103 from pin 2 on the EGRC connector. The battery voltage signal present at pin 2 on this solenoid never goes away or is taken to ground to operate the EGRC solenoid valve even when I rev the car quickly to 3K rpm in warm up mode.

If there is continuity from the EGRC solenoid valve to the ECM then either the ECM output transistor or switching device is not switching or something which causes the switch to occur is not satisfied. The diagnostic procedure does not state what is needed to make the ECM take pin 103 to ground. Apparently rpm changes over a short duration and other inputs such as engine temperature, etc must enter the algorithm which operates the ECM output for the EGRC solenoid valve. If you have any experience on this one, I'd appreciate a comment. I am fairly confident that there is nothing wrong with the EGRC solenoid valve itself since it measures 32 ohms and I can switch it when disconnected with test leads to the battery and the A, B, and C ports behave according to the procedure.

I have a sinking feeling the the ECM may be at fault.
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Old 07-24-2011, 11:33 AM
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The EGR solenoid should have 12 v positive+ when key is on. The ground side is controlled by the ECM. It may have to have some roadspeed to activate the solenoid , you know like maybe the car has to be moving and registering speed on the Vehicle Speed Sensor. (VSS) Many, but not all cars do. Subaru for one ,only needs a certain temperature to enable the EGR.
Did you check the resistance of the Solenoid coil?
Did you check for 12 v + at the solenoid plug?
Also check continuity from the ground side of the plug to the ECM connector
and check it with the ohm meter fastened to the circuitand with the ecm connector unplugged. Then go to the harness and wiggle it a little to simulate engine vibration. This is called a wiggle test. The Idea is that if a wire is broken it will cause the ohmeter to freak out rather than to stay steady as a good conductive circuit should be.
Also if the code is not erased first, the EGR solenoid wont run as the circuit fault code caused the ECM to shut down its operation to prevent the circuit problem from killing it. A circuit fault is anything outside the ECM, mostly like wiring or an electronic component such as a solenoid. It disables operation when a CIRCUIT fault is seen to protect the ECM.
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Old 07-24-2011, 01:08 PM
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EGR Harness Protector...

Thank you for the comments. I did the various checks as you mentioned since they were clearly outlined in the troubleshooting procedure. The tip on clearing the code prior to recheck in the event that the ECM is protecting itself is something of which I was unaware. That was not clearly outlined in the diagnostic procedure or was assumed. Thank you. Supposedly the vehicle did not have to be moving to operate the VSS but I did the engine rev in Park rather than neutral which may have been an issue. The procedure indicated neutral and I blew it off which may have been a mistake. I will retry the procedure since the speed factor may come into play if the engine is revved in neutral vs park.
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Old 07-24-2011, 02:51 PM
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Remember VSS is the vehicle speed sensor. It is measured at the axle or wheel speed.Not sure if it comes into play for egr operation but on many cars ( I think Nissan is one that it does) the strategy for EGR function does require the car to be moving.
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Old 07-26-2011, 04:55 AM
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P1400 problem...

Hello latech,
My comment about the VSS was not correct as you pointed out. I meant that the test for taking pin 103 to ground to activate the EGRC solenoid valve may have required "neutral" position of the shift lever rather than PARK where I did it to provide an rpm signal which may not be present with the manual lever in PARK. I have not rechecked it yet. I assumed NEUTRAL and PARK were the same thing but I'm sure there are plenty of differences.

I did measure the EGRC solenoid valve coil resistance and it was about 32 ohms which I have heard others comment upon as needing to be 30 ohms. I have also heard other values stated like 50 ohms, so I don't know the true value but I do know that it switches and the A, B, C ports flow per specification.

I thought it would be interesting to see what codes came back if I disconnected the EGRC solenoid valve and drove the car for a while. With the EGRC solenoid valve unplugged it was not possible to erase the pending code for P1400. I could get all codes to clear with the coil in the circuit but as soon as I unplugged the coil, the pending code P1400 reappeared.

The pending code will not erase with the coil disconnected. Thus if I erase the code with the coil connected and get PASS on the system I must leave the coil plugged in or as soon as it is disconnected and a READ is done, I get P1400 pending even though the car has never been run.

I never intentionally tried putting a fault on a car before to see how the DTC's would erase or display but I now am wondering if what I have said here is any clue to anything.

My last checks still to be done are to verify the true resistance of the coil by getting that information from somebody, redoing the rev procedure in warm up with the car in neutral, and checking the resistance of the wire from the ECM to the solenoid which I have also not done yet.

Does anything I have said here ring a bell? For this code to go away it seems that all that is needed is a coil of the right resistance connected to pin 103 of the ECM and battery power to the other side of the coil with the key on. What I am I missing?

It appears that when the code scanner does a READ, the devices connected to the ECM make a difference as to what codes are displayed during a key on engine off READ. I always previously thought that the DTC codes were stored memory in the ECM from what took place when the car was previously operated and not from anything done with the engine off and the key off.

This is what I read to understand something about pending codes:
OBD II Pending Codes are also referred to as “continuous monitor” and “maturing codes”. An intermittent fault will cause the computer to store a pending code in memory. If the fault does not recur within 40 warm-up cycles, the code will be cleared from memory. If the fault recurs a specific number of times, the code will then mature into a diagnostic trouble code (DTC) and the MIL or “check engine” light will turn on.
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Old 07-26-2011, 05:07 AM
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When you manually ground the circuit for the EGR solenoid , you should get action from it. There is no ned to have it in any specific gear, that is for operational strategy, not pinpoint diagnostics.Good question though.
Codes generate according to the severity or importance of the afflicted device. Some codes have a high priority and will trip a light as a code is generated, lower priority codes may set a code but not trip the Light.
I know it can be confusing, but You will have a light bulb moment sooner or later, I guarantee it.
The coil sounds right at 32 ohms but check the spec to be sure. Avoid hear say on things like that,And I have found that some programs for automotive techs have inccorect information as well , making it tougher.You can allways check another one against the one you have, be it a new one or one from the same kind of car.I like to refer to this as the Missouri Method or "show me".
Alldata is the best program out there in my opinion when it comes to technical info and support for a technician, a lot of the others ...not so much.
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Old 07-30-2011, 12:37 PM
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P1400 EGRC Solenoid Valve Circuit Malfunction, 2001 Nissan Altima GXE, 2.4 L

This is my last shot at problem:

I exhausted the checks on the EGRC solenoid valve circuit finding all wiring in tact and the solenoid valve of proper value around 30 to 35 ohms. I had to go to a Nissan dealer and measure the resistance of one off the shelf at the counter since I could not find it elsewhere. I was hoping that it would be significantly different from the 34 ohms of the one on my car. Not so!

Now, having exhausted the solenoid valve circuit itself, the only remaining prospects seem to be either the output stage of the ECM is not taking the EGRC solenoid coil to ground to turn it on, the proper input variables to the ECM not present, or the manner/logic/program in which the ECM produces an output is not taking place.

Having described this situation to the Nissan dealer technician, he related a virtually identical scenario and indicated that when they run into this, they have used complex scanning tools than the simple code reader and do a rather extensive procedure which I could only do with the equipment which I don’t have to do it. He deduced that it was either an ECM problem or some peculiar input issue.

If anyone has any advice on how to narrow this down any more, I have basically done the Factory Service Manual procedure which did not get into ECM or input issues at all.

The ECM sees the output circuit and I know it since I get a P1400 pending if I disconnect the EGRC solenoid valve without even running the engine and then do a READ. The ECM knows that the circuit is open circuited but it may not know if its own output transistor is not switching when told to do so which grounds the EGRC solenoid valve turning it on and shifting its valve spool when the other right inputs are received.

No advice here will be taken lightly! It’s either new ideas to try or off to the dealer. GEEZ! I hate when that happens. It seems like the cowardly way out but I just don’t have the gadgetry to get much further. I’d love to see the circuits for the ECM if they even exist. I do have the pinout information on the ECM but I can’t tell what inputs actually have anything to do with the EGRC solenoid valve being taken to ground other than general ideas from this article similar to my problem which begins on page 3...”CASE STUDY”
http://www.vcertt.org/news/11-02.pdf
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