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2005 ALDL connector resistance reading- pin C and D


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Searching for resistance (ohm) reading between C and D on the ALDL connector. It is the can high and low terminal, wires are white with red tracer and white with black tracer. Must be 2005 or 2006 with a MEFI 4B. Thanks

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You asked about this a few weeks ago.  I can't find any MEFI 4/4B manual that shows data on pins C and D.  They all show data on pin G (orange/black wire), and I presume that it is 8192 Baud similar to ALDL (OBD I).

PCM Manual, Page 173:  https://www.pirate4x4.com/d1/tech/billavista/MEFI/MEFI 4 & 4B DIAGNOSTIC MANUAL (L510005P).pdf

Indmar Manual, Page 61:  https://cdn.bakesonline.com/media/resourcelibrary/Indmar_MEFI4manual.pdf

Perhaps @COOP has a manual specific to 4B that shows something on pins C and D.

Do you have a specific problem that you are trying to solve (your last post said gauges)?  If you truly have a CAN bus, it should meet the CAN specification.

 

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Yes still trying to solve the gauges issue. Per Medallion when I had spoken to Scott, he said 2005 was the first year malibu used can bus from the ecm to the medallion gauges that are on j2- connector pins 9 and 24. of the mefi 4b,. not the single orange/back serial data line. On my 05, the can bus wires are spliced off the ecm pins 9 and 24 and go to the aldl connector as well which is C and D. With everything connected, I have 3 ohms at the can high/low on the aldl, I can disconnect the harness to the medallion, and i have 120ohm going to the medallion.  I've tried to get back in touch with Scott to no avail to see if that's correct reading on the medallion side. I only have 4 ohms at the aldl connector to the ecm with the harness disconnected.  I've talked with Larry at indmar, Bob at mefiburn, Technical services, and local malibu dealer. No one knows if the mefi 4b has 120 ohm resistor,. I know a little on the automotive side of can, and i would think the mefi ecm that uses can would be the same reading as automotive, but this is my first venture into the marine side. Sorry for the long post.

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Do you also have a data wire in pin G for scan tool use?  That would make sense if you do.

I would agree that 3 or 4 ohms on a transmission line is awfully low.  Anything between about 50 and 220 ohms would make more sense, and CAN specifies 120 ohms at each end (for a 60 ohm characteristic impedance on the bus).  This page mentions the concept of actively switched termination, which could be the case inside the ECM.

https://support.enovationcontrols.com/hc/en-us/articles/360038856494-CAN-BUS-Troubleshooting-Guide-with-Video-

If you have access to an oscilloscope, it might be useful to watch the signals and verify the voltages.

You didn't reply on your other thread, but making sure the cannon plug contacts are clean is a great first step.

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1 hour ago, justgary said:

You asked about this a few weeks ago.  I can't find any MEFI 4/4B manual that shows data on pins C and D.  They all show data on pin G (orange/black wire), and I presume that it is 8192 Baud similar to ALDL (OBD I).

PCM Manual, Page 173:  https://www.pirate4x4.com/d1/tech/billavista/MEFI/MEFI 4 & 4B DIAGNOSTIC MANUAL (L510005P).pdf

Indmar Manual, Page 61:  https://cdn.bakesonline.com/media/resourcelibrary/Indmar_MEFI4manual.pdf

Perhaps @COOP has a manual specific to 4B that shows something on pins C and D.

Do you have a specific problem that you are trying to solve (your last post said gauges)?  If you truly have a CAN bus, it should meet the CAN specification.

 

 

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I would be surprised if the ECM had active termination.  Can you pull it out and remove the cover to take a peek and buzz out the resistors inside?

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Yes, I do have the serial data wire on pin G as well. I have a laptop with mefiburn software installed. I can read all the parameters within the ecm. ( it reads off the ground and serial data line) I have used a labscope as well, very spikey wave pattern, nothing I've ever seen before, not a square wave like automotive can. I have had no workings with baud rate, is that the same as can? I did notice in the software in the ecm it said 8192 baud. I don't know if you saw my original posts from last year, I bought this boat not running, with a bad ecm. I purchased a reman ecm from my local malibu dealer, and at that point the gauges that read off the can lines would not register, other gauges do work. ( fuel, tach, speed in the perfect pass). I called and talked with the dealer after i bought the ecm, basically was told not there problem, and offered no help beyond them selling me the ecm. If someone could verify should there be 60 ohms at the aldl connector pin C and D or not would help. That would let me know if the ecm actually has a 120 ohm resisitor on pin 9 and 24. I appreciate your help. I may just send the ecm  to have checked. 

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38 minutes ago, Kelley1 said:

 

i did see the one from bakes, but its from 2003, and the mefi ecm did not have can on malibu until 2005, thats why pin 9 and 24 is blank, in 05 its the can high and low pins

Edited by Kelley1
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What is the resistance between c and d, the canbus wires.

Im a bit rusty on canbus, but i think it should be 60ohms. If not (like its 120ohms) theres a break in the canbus lines, or a faulty canbus device. I believe the paddle wheel, and temps sensors are on the canbus lines as well. If just one item on a canbus circuit is malfunctioning it will take down the whole system.

Ill have to do a bit of checking if Im wrong, ill check with my lead tech as well.

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Coop, everything connected, everything turned off, C and D are around 3 or 4 ohms, i can unplug the engine to boat harness and I have 120 ohm to the medallion computer from the boat harness connector. I only have 3 or 4 ohms at the engine harness connector to the ecm. I have checked direct to the ecm as well, same result. What Scott at medallion told me, was the speed. (for the speedometer),  hours, coolant temp, volt and oil psi read from can low and high. That is all on the can lines. He said this started in 2005. Tach, speed for perfect pass, fuel level, lake temp, air temp etc. reads off other data lines and all those are functioning correctly. Thanks for the help

Edited by Kelley1
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22 minutes ago, COOP said:

What is the resistance between c and d, the canbus wires.

Im a bit rusty on canbus, but i think it should be 60ohms. If not (like its 120ohms) theres a break in the canbus lines, or a faulty canbus device. I believe the paddle wheel, and temps sensors are on the canbus lines as well. If just one item on a canbus circuit is malfunctioning it will take down the whole system.

Ill have to do a bit of checking if Im wrong, ill check with my lead tech as well.

Checking one end (with the rest of the harness removed) will show you only the one resistor, so 120 Ohms.  Checking at a data drop (e.g. at the paddle wheel) in a complete bus should show you both resistors (120 Ohms each, one at each end, for 60 Ohms in parallel across the + and - lines).

2 hours ago, Kelley1 said:

Yes, I do have the serial data wire on pin G as well. I have a laptop with mefiburn software installed. I can read all the parameters within the ecm. ( it reads off the ground and serial data line) I have used a labscope as well, very spikey wave pattern, nothing I've ever seen before, not a square wave like automotive can. I have had no workings with baud rate, is that the same as can? I did notice in the software in the ecm it said 8192 baud. I don't know if you saw my original posts from last year, I bought this boat not running, with a bad ecm. I purchased a reman ecm from my local malibu dealer, and at that point the gauges that read off the can lines would not register, other gauges do work. ( fuel, tach, speed in the perfect pass). I called and talked with the dealer after i bought the ecm, basically was told not there problem, and offered no help beyond them selling me the ecm. If someone could verify should there be 60 ohms at the aldl connector pin C and D or not would help. That would let me know if the ecm actually has a 120 ohm resisitor on pin 9 and 24. I appreciate your help. I may just send the ecm  to have checked. 

Put the scope "ground" lead on the - bus wire and the scope probe on the + bus wire to get rid of the spikes.  CAN is a differential bus, so it basically doesn't have a low impedance path to ground, which means that the spikes will show up if you let the scope use an arbitrary reference.  Once you look across just the - and + wires, you should see nice square waves that are a bit less than 5V.  If so, the bus is probably OK.

I suspect that you will need to load the correct software into the ECM to wake up the CAN bus.

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8 minutes ago, justgary said:

Checking one end (with the rest of the harness removed) will show you only the one resistor, so 120 Ohms.  Checking at a data drop (e.g. at the paddle wheel) in a complete bus should show you both resistors (120 Ohms each, one at each end, for 60 Ohms in parallel across the + and - lines).

Put the scope "ground" lead on the - bus wire and the scope probe on the + bus wire to get rid of the spikes.  CAN is a differential bus, so it basically doesn't have a low impedance path to ground, which means that the spikes will show up if you let the scope use an arbitrary reference.  Once you look across just the - and + wires, you should see nice square waves that are a bit less than 5V.  If so, the bus is probably OK.

I suspect that you will need to load the correct software into the ECM to wake up the CAN bus.

 

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Yes, reading on the 5v scale, ground and test leads properly terminated, spikey- not nice square forms opposite of each other. If the mefi is the same as obd2 reading, then the ecm is the issue. I've checked and unplugged all the sensors, same result. I have not checked at the paddle wheel, but with the can lines going to the aldl, if everything is correct and functioning properly, shouldnt i be getting 60 ohms on c and d? just like i would on obd2 can pins?

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2 hours ago, Kelley1 said:

Yes, reading on the 5v scale, ground and test leads properly terminated, spikey- not nice square forms opposite of each other. If the mefi is the same as obd2 reading, then the ecm is the issue. I've checked and unplugged all the sensors, same result. I have not checked at the paddle wheel, but with the can lines going to the aldl, if everything is correct and functioning properly, shouldnt i be getting 60 ohms on c and d? just like i would on obd2 can pins?

On thinking about it more, I agree that you should see 60 Ohms on C and D.  I was thinking that you had disconnected the ECM at its own connectors (J1 and J2) and expected to see 60 Ohms.  Pull J2 and check the resistance from Pin 9 (CAN-) to Pin 17 (CAN+).  If that looks like 120 Ohms, then check your harness to make sure that your C and D pins are connected correctly to 9 and 17 on J2.

Reference:  https://www.aimtechnologies.com/support/racingecu/Delphi_MEFI4B_102_eng.pdf

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2 hours ago, Kelley1 said:

Yes, reading on the 5v scale, ground and test leads properly terminated, spikey- not nice square forms opposite of each other. If the mefi is the same as obd2 reading, then the ecm is the issue. I've checked and unplugged all the sensors, same result. I have not checked at the paddle wheel, but with the can lines going to the aldl, if everything is correct and functioning properly, shouldnt i be getting 60 ohms on c and d? just like i would on obd2 can pins?

Maybe strike my last post.  I just found this on this site, and it makes more sense than most of the stuff I have seen.  The MEFI 4B pinout shown here indicates that CAN- is J2-9 and ALDL D, and CAN+ is J2-24 and ALDL C.  Check for 120 Ohms between those two, and if they are OK then verify your harness.  It is possible that your new ECM has a different pinout than the old one, so you may need to move a few sockets around.  Anyway, this looks plausible, as does the wiring diagram included.

 

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thanks justgary, if in fact the mefi should be 120 at 9 and 24, then i know its the ecm fault. that's what i'm trying to verify if it is supposed to have 120ohm. if it does carry 120, then i should have 60 at the aldl. that is the way the automotive circuit reads, i wasn't sure if the marine ecm would be different.

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1 hour ago, Kelley1 said:

thanks justgary, if in fact the mefi should be 120 at 9 and 24, then i know its the ecm fault. that's what i'm trying to verify if it is supposed to have 120ohm. if it does carry 120, then i should have 60 at the aldl. that is the way the automotive circuit reads, i wasn't sure if the marine ecm would be different.

The bus should meet the CAN specification.  Even if the ECM doesn't carry the terminator inside (for example, they could put it into the connector), it should then be high impedance (about 30,000 Ohms or so) since it would be a drop off of the bus, similar to the sensors.  Nothing should be 3 or 4 Ohms.

Check (and report back here, if you care to) the following if you can:

1- Resistance of ECM from J2-9 to J2-24 with J2 disconnected.

2- Resistance of ECM connector J2-9 to J2-24 with J2 disconnected.

3- Wiring from J2-9 to ALDL-D and J2-24 to ALDL-C (should be zero Ohms with J2 disconnected).

4- Voltage from ALDL-C to ground with J2 connected and ECM powered (engine running is OK).  Should be ~2.5V.

5- Voltage from ALDL-D to ground with J2 connected and ECM powered.  Should be ~2.5V.

6- Voltage from ALDL-C to ALDL-D with J2 connected and ECM powered.  Should be ~4V.

7- If you can get an oscilloscope on it, a photo of the trace with scope ground on ALDL-D and scope probe on ALDL-C.

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Justgary, the readings are follows 

1-4.2

2- 0,    120 with the boat harness still connected

3- 0

4- .15v

5- .14v

6- 0v

7- didn’t bring my Scan tool home tonight to check

 

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1 hour ago, Kelley1 said:

Justgary, the readings are follows 

1-4.2

2- 0,    120 with the boat harness still connected

3- 0

4- .15v

5- .14v

6- 0v

7- didn’t bring my Scan tool home tonight to check

 

What is the chance that they sold you a 4A instead of a 4B ECM?

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It’s a 4a they said they converted to a 4b, bought from Malibu but came from mefi burn / Obd diagnostics , I sent it back to bob at mefi burn right after I got the ecm, he said everything was correct, that’s why I been chasing other areas to repair the gauges,

Edited by Kelley1
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If they insist that it is correct, I would put an oscilloscope on it again and take a look at the output with it in the harness.

By the way, your 0.15V across 4.2 Ohms uses about 0.035A (35 milliAmps), which is about what I would expect the ECM to limit current to.  That 35 mA across 60 Ohms would be about 2.1V, or pretty close to what we expected.  It sure seems like they have the wrong resistors in place in the ECM....

Are you comfortable taking the back off of the ECM and looking inside?  Maybe we can see the resistors and measure them directly.

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