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Jeremy, Certified Truck/Bus Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 3362
Experience:  ASE Med/HD Truck Technician, NATEF Diesel Engines and Electrical/Electronics Technician, EPA 608/609 HVAC Certified, Steering/Suspension and ABS/Brakes Technician
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I have a 2003 sterling acterra with the Mercedes 4cyl turbo

Customer Question

I have a 2003 sterling acterra with the Mercedes 4cyl turbo diesel engine, recently engine light came on and oil pressure gauge stays at 100%
And engine temp gauge doesn't read either
diagnostic screen shows 5 codes
- oil temp sensor short to ground
- oil pressure sensor short to ground
- turbo pressure sensor short to ground
- engine coolant temp sensor short to ground
- intake manifold sensor short to ground
Engine still runs fine but obviously with no turbo there is no power, I'm at a loss as to where to start and even dealer won't give me any diagrams
I need some help as to what they all share like power or ground source ,possibly what fuse or relay they share
pls already been dowe over a week and rapidly losing work and position within the company
Submitted: 2 years ago.
Category: Medium and Heavy Trucks
Expert:  Pete replied 2 years ago.
My name is ***** ***** I am a professional here at Just Answer. I noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.
My info is limited on your model here but I see no one else has responded and thought I would see if I can help here.
I don't have the diagram info here you are looking or but I see no one has responded with help so from what I can tell here it looks like some of your engine wiring is shorted to the body,engine or frame.
Inspect all engine wiring for any shorted wiring and repair any that are found at fault here.I have seen in several cases before where the wiring shorts like this here and needs repaired to correct this fault.
Thanks Pete
Customer: replied 2 years ago.
I have unplugged the ecu harness on the driver's side of the engine and used a meter and continuity tester with it grounded to engine to frame ground wire ,test on every pin
on the harness (wire side) with no indication of any wire having continuity with the
engine/frame ground so no wires short or rubbed through on harness to engine side !
Now on ecu side where harness plugs in , tested all pins many have bright continuity signal with the engine ground (expected )
Then there are a few with absolutely no signal
and a few with faint signal but definitely a signal , so what i need is a diagram or
print/pin out of the harness and ecu
or any other suggestions would be great
Expert:  Pete replied 2 years ago.
Unfortunately since I do not have the diagram info you need here and you see no grounded wiring I will have to open your question up for others here to see if anyone else can assist further on this.
I will have to open this question up for others here to see if they can assist further on this as someone else here may have more info on what to check or do with this issue.I hope you can get this resolved with ease.No need to reply to my last post here unless it is a last resort as it will keep your question locked to me and others will not be able to view it.
Thanks Pete
Expert:  Jeremy replied 2 years ago.
My name is ***** ***** I will assist you with your concerns.
Can I get the full VIN of the vehicle so I can pull the workshop books and diagrams for you?
Expert:  Jeremy replied 2 years ago.
Customer: replied 2 years ago.
So I'm currently working on the truck tried everything I can think of, in my testing i found that all the red wires directly off the back of the ignition (about 5 or so ) create a circuit to ground? ?? Any idea on what to do next? ??
Expert:  Jeremy replied 2 years ago.
All of the wire go to ground? That isn't correct...
Wires should be:
power in
There shouldn't be all of them to ground.
With all those codes that you are having, I'm leaning on you having a ECM problem or a engine harness problem. What you will have to do is actually do a ohm test on each of those circuits you are getting the shorts on and see if they are ohm above 1k or if there is another issue. It's frustrating. I know, I do this every day, but all you can do is go wire by wire, circuit by circuit.
The only common is the harness plug going to the ECM and the ECM for all those circuits that you have codes on. The ground for this engine and ECM is at the starter. MBE and Detroit love using the stater for the engine grounds. So you can see if there is a issue there at that connection, but i doubt it is a ground issue for you would be getting more codes and maybe even a non running engine.
With you already checking for short to ground with continuity test, I would lean on this vehicle having a ECM issue, especially with all those sensor codes. They don't all fail at once with a short to ground unless the short is in the harness or in the ECM. This is what I;ve learned over the years. The ECM doesn't send power on it's internal switches. It sends grounds so you will get short to ground codes and not short to power when they fail. Short to power of high voltage is usually always harness related. I am thinking this issue is ECM related.
Customer: replied 2 years ago.
i unplugged the ecu completely both harness,
i then ground my meter to engine to frame ground, test each wire in the harness for continuity to ground am i correct in saying that the meter should read 0 or beep at me ?
Can you pls explain how to test the ecu its self
As well as having the battery totally disconnected
thx for your help i will be glad to accept you answer if we can figure this out
Expert:  Jeremy replied 2 years ago.
The only way to test the ECM is with the software or on another truck. All you can really test is the signal wires going in and coming out of the ECM to verify that you have a good connection. The tests you did with the meter on the frame is just checking to see if there is a ground issue from the wire to the frame, but you still need to do loop back tests. Like for the oil pressure sensor, you put one side of the meter going from the ECM and then another on the wire coming back and check for high ohm readings or no reading to indicate a break in that wire. Really high means there is interference on that wire or the sensor is bad. You then move to the MAP sensor and check that. If they all test good, then you move to the output signals to the gauges, but this time you do that with volts. You actually put a pin tester into the connection of the wire and verify you have voltage leaving the ECM and going to the gauge. IF there is a signal, the issue is towards the luster. However, you are getting errors on the loopback from the sensors themselves based on the codes you have and therefore, those are the issue and not the gauges or you would have a code for the cluster.