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Engine 5.0 OSiF(F) with 90 pin emc connector. Schematics show…

Engine 5.0 OSiF(F) with 90...

Engine 5.0 OSiF(F) with 90 pin emc connector. Schematics show the drive trim sender input going to pin 46 on the 90 pin connector and then being routed out on pin 86 going out to the 10 pin engine connector and on to the trim gauge. Question is what is the ECMs role in the receipt and transmission of the signal before it is sent on to the trim gauge?

The trim sender provides a variable resisitive reading for the trim gauge and I do not understand why it is being sent to the ECM and then resent to the trim gauge. Does the sender input need to be of a certain ohm value such as 10 ohm or 11 ohms in order for the ecm to send info to the trim gauge to indicate the overall up or down status?

The trim gauge will not register a down position if the trim input is grounded to the ecm which is equal to Zero Ohms and is necessary to have the trim gauge register a down position. Does the ECM require a low ohm value in order to output a signal to the trim gauge? If not then what is required for the ECM to send data for the trim gauge, in order to properly register the drive trim position.

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Answered in 9 hours by:
3/16/2010
Marine Mechanic: John White, Marine Mechanic replied 12 years ago
John White
John White, Marine Mechanic
Category: Boat
Satisfied Customers: 306
Experience: 11 years experience working on outboards, inboards, sterndrives & pwcs
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The trim gauge circuit does go through the ECM, but the ECM doesn't control anything or send a signal. The ECM is basically in the circuit to monitor the circuit. The ECM can set a code if the circuit becomes open, shorted to ground or shorted to a power source.

 

If you're having trouble with the trim gauge there are a few things you can try. Start with the gauge itself. Disconnect the sending wire from the back of the gauge. At this point the gauge should be reading full up with the ignition switch turned on. Use a piece of wire to jump between the send and ground terminals. The gauge should swing to full down with the jumper in place. If it fails either of these tests the gauge is bad.

 

Other than the gauge you can check the resistance coming from the sending unit. Unplug it where it plugs into the engine wiring harness. Use a multimeter to measure the resistance between the two wires going to the sending unit. With the outdrive fully down should be 10 Ohms. As you trim the drive up you should see the Ohms climbing steady and evenly. Once the outdrive is fully up it should be 167 Ohms on your meter. There is some adjustment at the sending unit, so if it's just off a little it can usually be adjusted.

 

If the gauge and sending unit pass then the problem is in the wiring or possibly even in the ECM itself. You would need to test continuity from pin 46 on the 90 pin ECM plug back to the plug in for the sending unit and then test continuity from pin 86 back to the dash. If the gauge, sending unit & wiring check out then you would know the problem is the internal circuit in the ECM. Just let me know if you have any other questions.



Edited by XXXXX XXXXX on 3/16/2010 at 3:06 AM EST
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Customer reply replied 12 years ago

Since I have previously performed all the conitunity checks you have stated above I have to assume that the ECM has a problem. However there is no DCT code that is listed for a faulty Trim sensor signal (open or grounded), at least not in the info I have.

 

Does the ECM require at least 10 ohms to 167 ohms be received on the sender signal line (pin 46) to pass the output to the trim gauge from (pin 86)?

 

Based on the above statemsnt = Does opening or grounding the sensor output to pin 46 prevent the ECM from outputting a signal to the trim gauge on pin 86?

 

I tried grounding the sender input to pin 46 while the ECM was fully connected in the circuit and did not get any response or movement from the trim gauge. Removing the ECM Connector and shorting pin 86 to ground caused the gauge to go to the full down position (Note: Ignition Key was turned on after all connections were made to establish system response).

 

If I bypass the ECM - I assume that a signal wire direct from the sender to the trim gauge will provide the data/info for the drive trim position gauge and their will be no effect on the ECM since all it has to do is pass the data input from pin 46 to pin 86 All I will loose is a DCT code, if such a code is available to be read out from my ECM.

 

Additional Thought = Does the ECM trim signal, if ECM is working properly, use an open sensor input to limit engine speed (Switches engine speed to protected mode same as an overheat condition or low oil pressure) due to open being sensed as a drive in full up position OHM value greater than 200 ohms. if a ohm value between 10 and 167 is required for ECM Output to pin 86 there would be no signal passed to the trim gauge for position of outdrive and the trim gauge would indicate full up position with an open.ckt sensed

 

Additional thought = A grounded signal would therefore indicate the drive is in full down position. If a ohm value between 10 and 167 is required for ECM Output to pin 86 there would be no signal passed to the trim gauge for position of outdrive and the trim gauge would indicate full up position even though the ckt was grounded and the drive could be up or down or some position in-between. As a further note all ground connections in the affected circuit are good.

Marine Mechanic: John White, Marine Mechanic replied 12 years ago

The ECM doesn't have any control over the trim gauge circuit, nor does it use a problem in the circuit to change the engines running characteristics. It does the same thing on the circuits going to the water temperature and oil pressure gauges. These are analog signals so the ECM doesn't control them. If there is a problem in one of these circuits it will set a code in the ECM and the malfunction indicator lamp will come on if one is installed. According to the manual there are 2 codes for each gauge - open / short to ground or short to power. The ECM will not put the engine into safe mode and no audible alarm will sound if there's a problem in one of these circuits. There are other circuits the ECM monitors for the actual oil pressure and water temperature and they can effect the running characteristics of the engine (safe mode).

 

Another thing to check that I didn't mention was to make sure there is no power on the trim gauge circuit. What you can do otherwise just to test would be remove the sending wire from the back of the gauge and unplug the sending unit connector from the engine wiring harness . Use a temporary piece of wire to connect to the back of the gauge and run back to the sender connector. Use another short piece of wire for the ground side of the sender and connect it to the negative side of the battery or just a good ground on the engine. Make sure this gauge is grounded as well. This is the long way for testing, but it ensures the gauge and sending unit are functioning correctly. You are bypassing the ECM this way as you mentioned, but without having to cut into any of the wiring harness.

 

You can bypass the ECM this way permanently, but the ECM will always have the code stored for this circuit if you do & if the malfunction indicator lamp is installed then it will always be on indicating this failure. It would not effect how the engine ran or cause an audible alarm, but it would just be a patch for the actual problem.

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Customer reply replied 12 years ago

Then I guess that the real fix is to replace the ECM? That is an expensive thing to do just to have the trim signal routed through the ECM.

 

My fix is to run a new wire from the trim sender output to the trim gauge and leave all other wiring as is, including wiring to the ECM pin 46 and from the ECM Pin 86 to the engine harness 10 pin connector and then to the trim sender . The only wires that would be disconnected is the sensor input to Pin 46 on the ECM and the sensor wire at the back of the trim Gauge . If the ECM goes totally out and needs to be replaced then the wire from the sensor to the gauge will just be removed and the sensor hooked up to the existing pin 46 wiring and the pin 86 wiring which goes to the gauge. I did this using a new single wire and the trim gauge works as it should. Any other thoughts before I accept the answer. - Thanks

Marine Mechanic: John White, Marine Mechanic replied 12 years ago

It sounds like your problem is in the ECM based on testing everything else and the fact that it now works with the circuit through the ECM bypassed. I can tell you if a customer came into the shop with this issue I would do exactly as you have done. I would not replace the ECM over something this small as this because will not affect the running of the engine in any way. Any time the ECM is scanned you will have the code appear, but it's no big deal. All other alarms will still function normally, most importantly hard codes which will set the engine into safe mode.

 

Since the trim gauge is working properly I wouldn't worry about it. I honestly have no idea why Volvo built the system this way as anything that would cause a code for any of the gauges would also keep the gauge from working. I think they just went a little over kill on the diagnostic system.

John White
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Experience: 11 years experience working on outboards, inboards, sterndrives & pwcs
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