czarcaps

My ML is running between 40-80c. I get a code po115 engine coolant temp circuit. replaced thermostat,sensor,clutchfan,waterpump,auxillary pump(secondhand) yet I get the message. checked voltage output on coolant sensor connection. I read 0.3 volts. Is this normal?

Id like to rule out wiring harness short. So can anyone provide me with the ECU pinout and voltage output of coolant sensor.

Or am I missing something?? Anyone please send me a reply

Maj. Dundee

Before we get on to the tests, have you cleared the code with a scanner?

czarcaps

i. did. drove a couple of miles and it. came back. d the. ke on off method i read 0,3 at
the wire connector to ecu..

Maj. Dundee

Please explain what the key on off method is.

czarcaps

I had a volt meter reader poked @ connector. With key off = 0 volt , with key on= 0.3 volt. Do you have specific volt information and pin number for the engine coolant temp sensor??

Maj. Dundee

Test must be conducted at the ECM and the ETC, according to coolant temperature. Wire numbers and their colors are supplied.

czarcaps

Thanks for the diagram but where do I stick my voltmeter as far as the ecu connectors are concerned. I see abcd connector. I'm kinda dumb on this

Maj. Dundee

There is black plastic covering each connector with a small wire tie at the end. Cut the wire tie and remove the covering.

czarcaps

Is N3/10 the pinout ill be looking for in connectors? is it on connector a b c or d? I have not opened it. Ill be working on it this weekend. Are the pinouts labeled?

Maj. Dundee

You were the one who asked repeatedly for these test and now I'll be married to this thread until it's done,
.
Have you opened the pdf ECM Connectors? It clearly shows that there are 6 connectors labeled A to F and all the pins are numbered.

czarcaps

Sorry Maj. you are the best.. I did have an idea what ill need to do but am not sure if the pins are actually labeled N3/10 . I have not opened it yet. Way back late 1980's usually if they said N3/10 it would mean connector N @pin 3/10. but here connectors are A-F, no N. I will open it this weekend and study it further. hope i get it right. Thanks for your patience.

Maj. Dundee

N3/10 means the ECM.

The pdf diagram shows the layout of the connectors. You only have to work with conn. E in the first test. Cut the small wire tie, remove the cover and all the wires and pins will be exposed.

Fan out the wires and in relation to the new illustration below, find wires 28E and 29E, making sure that they are the same colors that are supplied in the test.

czarcaps

News Flash!! My voltmeter reads 0.3v @50-60 c my ohms read 700+/- . Confirmed its not my harness.. i got same reading when tested the connector at sensor side. A verdict of ECU fault is now favorable. Is there any other tests Ill need to do before i pass thisverdict. Damnn im looking @ 500-600$ on this.

czarcaps

My voltmeter probe is kinda big to get into the ecu connector. I used sewing pins. Stuck it into the holes and probed it from there..lol. old school trick i learned from someone.

Maj. Dundee

czar, you are not making this easy for me. I can't guess or assume what test you are conducting.

Open the tests again. They are numbered 8.0, 8.1 & 8.2. You must tell me the results of each test.

8.0 @ ? °C -result is what voltage

8.1 @ ? °C -result is what Ω

8.2 @ ? °C -result is what Ω

czarcaps

8.0 @ 50c = 0.3v
8.1 @ 50c = 700 ohms
8.2 did not perform . was already sad with 8.1 test result

Maj. Dundee

Retest when the eng. is completely cold. Remember that 50°C=122°F.

Aside from you being aggravated or discouraged,it is also up to you to complete all three tests.

czarcaps

finally did a retest..engine cold cali weather@ 66c... test 1 key @ on position voltage reading at 0.4v test 2 engine key off reading 3000+ohms test 3 3000+ ohm. Can i just buy a used ecu same model and slap it in there? Now im confirmed a sad person with a sick ecu

czarcaps

For a replacement ecu. Do I just need to go with the part number on my existing . Or do I still need to do. Some programming / flash ecu ?

Thanks maj

Maj. Dundee

First of all it is not the outside temp. that you are looking for, it is the temp. of the coolant/engine.

Secondly, ohm readings are testing the wires, not the ECU. You do not need and ECU.

czarcaps

That's correct. With my engine cold. I should be at least be getting 3v. But I am getting a 0.4v. This is a voltage of a hot engine. My obd2 scanner reads -40c. But that reads off the temp sensor voltage feedback..which is questionable due to my suspected ecu voltage supply inaccuracy. So with engine cold. Not cranked at all. First thing in the morning after overnight park In Garage . These were my readings. Ohm reads consistent . If it's not ecu, what else could it be?

czarcaps

To replace ecu do I just go by the ecu part number or do I still have to flash ecu. . Thinking of getting used one

Maj. Dundee

If you want to replace the ECU go right ahead and do so. Just match the number on it.

Just to check how you made the voltage test. I don't know what type of meter you have, digital, auto ranging, but I hope you had it on the correct scale.

You originally said that you got a 0.3v, if you didn't have it on the correct setting, that could mean it is actually 3.0v

czarcaps

good question major . I had the digital meter set at the 12v setting. pls advise if not right so I can retest. tester settings are 1.5 v 6v 9v and 12v.

Maj. Dundee

It's supposed to be set on the 12v scale, but how you conducted the test I do not know. You have to make sure that you have the correct wire colors in the correct position.