ECU repair

[mechanic_]

Hello,

This is my first time posting here

I joined the forum to ask a question about ECU repair.

My Bosch MP5.2 ECU is defective. The issue is that the car is very old, and I’m unable to find a replacement ECU in my country.

At this point, my last option is to try repairing the ECU. I have previously worked with ECUs (cloning data and doing immo off), but I have never actually tried diagnosing a hardware fault.

Does anyone here have experience with repairing this ECU? Is it generally repairable, and if so, what are the common things that should be checked?

Thanks in advance.

 

[danadak]

Have you lookked at some of the videos over here : https://www.youtube.com/results?search_query=ecu+repair

Non specific to your version but general principles apply.

 

[mechanic_]

Thanks for the reply danadak. I have watched some videos on YouTube on testing ecu components like resistors, capacitors, transistors... I tested it all, but still didn't find what is faulty. Maybe some integrated circuit that I don't know how to test.

 

[danadak]

Also if you can get access to a good optical inspection scope look at soldering, amazing
how much stuff made with marginal solder joints. Look for cracks, areas where solder
does not appear to have "wicked" onto the leads/joints. Both sides of board.

poor solder examples at DuckDuckGo

DuckDuckGo. Privacy, Simplified.

duckduckgo.com

Capacitors historically # 1 problem, they age, as well as carbon comp R's (especially ones
exposed to continuous heat).

Connectors and cabling always suspect, especially in high vibration environments like a vehicle.

Is the ECU entirely dead ? No OBD access to it ?

 

[narkeleptk]

Hello,

This is my first time posting here

I joined the forum to ask a question about ECU repair.

My Bosch MP5.2 ECU is defective. The issue is that the car is very old, and I’m unable to find a replacement ECU in my country.

At this point, my last option is to try repairing the ECU. I have previously worked with ECUs (cloning data and doing immo off), but I have never actually tried diagnosing a hardware fault.

Does anyone here have experience with repairing this ECU? Is it generally repairable, and if so, what are the common things that should be checked?

Thanks in advance.

What are your issues with car and what is it that you suspect the ecu is doing/not doing?

 

[mechanic_]

@danadak @narkeleptk
I don't have spark, no fuel pump relay clicking, can't connect to diagnostics, and I have no 5V reference on the crank sensor. ECU has all grounds and powers.

 

[mechanic_]

I have tried to heat the ECU a little bit with a heat gun to check if it has bad solder somewhere, but didn't fix it.

 

[danadak]

Per chance do you have a low V Capacitor checker ? They apply a couple 100 mV level of AC
and look for ESR, and exceedingly low ESR is a short in effect.

https://www.youtube.com/results?search_query=low+esr+capacitor+tester

The orginal classic https://anatekinstruments.com/products/fully-assembled-anatek-blue-esr-meter-besr

 

[narkeleptk]

Considering the symptoms, it sounds like the ECU is completely offline. I've never worked on one of those here in the States, but it looks similar to some older EU cars we have here.

First, I'd identify the external connections for B+, IGN/RUN, and ground from wiring diagrams. If possible, also identify the diagnostic communication lines so you can see whether the ECU attempts to communicate on the bench. Apply power and monitor current consumption while on bench. You should see a noticeable change when IGN/RUN is applied. If there is little or no change in current draw when switching IGN/RUN on and off, I'd suspect the ECU is not booting at all.

Based on the symptoms, my internal troubleshooting would likely go:

1. B+ and IGN/RUN input conditioning and filtering circuits (capacitors, diodes, protection components). Given the age of the unit, failed capacitors would be one of the first things I'd check.

2. 5V regulation. If the 5V rail is missing (power for logic circuit and external sensors), determine whether the fault is the regulator itself or an issue with its inputs, enable circuit, or supporting components.

3. If necessary, inject a clean external 5V supply while still providing the normal 12-14V inputs and monitor current consumption. This can help determine whether the ECU will begin booting with a known-good 5V rail.

4. If the ECU still does not boot, investigate the MCU directly. Verify power, reset, clock, and any required enable signals. I'd also read the eeprom and flash memory to rule out data corruption.

Since you said you can clone, maybe you should try and pull eep/flash first as back ups. Also, download some other mp5.2 files and compare them to help verify if software or hardware issue.

 

[mechanic_]

I don't have an ESR tester, but I'll try to buy one in the near future. I checked all the capacitors using a multimeter in capacitance mode, and their measured values are within an acceptable range.

 

[mechanic_]

I have identified the 12V supply and grounds. I also found the K-line. The ECU has constant 12V, ignition 12V, and three ground pins. I tried bench testing and diagnostics on the bench, but it didn’t work. I measured the current draw a while ago, but I don’t remember the exact value—only that it was just a few milliamps.

 

[mechanic_]

Here is the picture of my ECU.

 

[bertus]

Hello,

I see a couple of those yellow tantalium capacitors.
Those tend to fail as a short circuit.

Bertus

 

[mechanic_]

Hello Bertus. Already checked. Its not short ciruited. Thank you for reply. ))

 

[narkeleptk]

it was just a few milliamps

It probably should be around 200 to 300 mA with RUN applied. Seeing only a few milliamps supports my original post that it is not waking up. I would continue tracing the input power and then power rails for logic supply.

 

[mechanic_]

Thanks man.

 

[Sunnysky]

- with power, the CPU crystal has 2 pins input and output. When measuring on DC both should be roughly half of the chip V+ to ground. On Vac the output should be a full scale square wave , will be x Volts. and not near 0 mV. This is essential. You can inspect the solder for a hairline circular solder break if 0Vac.
If clock is running, Look for active voltages without shorting pins to see if CPU is enabled or alive.

Next look for voltage regulators like 3.3V, 5V physically opposite Pin 1 dot. or look up part number schematic.

 

[mechanic_]

Thanks for advice SunnySky. ) I will post if i found something

 

[danadak]

The xtal osc can be sensitive to probe loading, so just bring probe tip close to
osc C's or xtal, scope on roughly 100 mv box to see if its running. Probe at 10X.

Can you identify the pin that puts ECU to sleep ? Any documentation on it ?
Have you asked ChatGPT to try to find more docs or pdf's on it ?

 

[mechanic_]

Yes i asked chatgbt, but didnt found anything. I will do a little more research