Published: 2022-01-26
MECHANIC: We have a problem with starting the engine in an Opel Meriva B, this is a car from 2012 – it's ticking and it sounds as if the battery is weak, even though the battery is new...
| EXPERT: | What engine? |
| MECHANIC: | 1.4 petrol, 103 kW. |
| EXPERT: | Ok, what exactly is the situation? |
| MECHANIC: | We can't start it, it behaves as if the battery is weak, I mean, the starter motor is not working, we can only hear the ticking of the electromagnet. Also... we checked the wiring and we found out that there is not enough power from the engine controller to the starter relay. And not only that, the battery we put in is brand new, but when the car stays overnight, in the morning when I go to start it, the starter clicks, but if I connect a second battery in series then the car starts with no problem. |
| EXPERT: | This means that either you have no ground on the engine or you have a high-current cable that is defective. |
| MECHANIC: | Yeah, but if I check the voltage with a meter, everything is correct on the cables. |
| EXPERT: | You can't check the voltage at the battery. You would have to check for a voltage drop between the positive cable, the positive post, and positive terminal at the starter. And you would have to check the ground, between the negative cable, the negative post of the battery, and the starter ground, but measure the voltage while cranking. |
| MECHANIC: | But if I apply extra current to the starter the same thing happens. It looks like there's a weak battery, but the battery is brand new. If I apply extra current the car fires. This is when it's cold though, if the car is parked in a warm garage there is a chance that it will start on the installed battery only. |
| EXPERT: | But the starter relay works? |
| MECHANIC: | The starter relay... Yes, it's working, but there's nothing at the moment that... When the starter solenoid clicks, there is no full 12 volts from the engine ECU to this relay that turns on the control... |
| EXPERT: | Okay, hold on. The relay is being energised, the one which is applying current... to the starter solenoid I understand, right? |
| MECHANIC: | Yes, exactly, yes. |
| EXPERT: | Is there current? |
| MECHANIC: | Yes. |
| EXPERT: | Then what does the rest of it have to do with anything? The starter should be turning already. |
| MECHANIC: | I mean... The relay behaves the same as the solenoid, it fluctuates all the time. |
| EXPERT: | Oh, the relay. So the relay doesn't have a sustained voltage and doesn't supply the proper current to the starter solenoid. |
| MECHANIC: | Yes, exactly. And the pulsating current goes from the relay to the electromagnet on the starter. The wiring loom, we checked everything up to the controller, the resistance of the wires and connectors, conductivity... it's ok. |
| EXPERT: | And when you short-circuit the relay from the starter, does it spin or not? |
| MECHANIC: | Well, if I energise the relay through the test light, through the bulb type tester, the starter runs without any problems. So obviously there is no 12 volts from the engine control unit going to the relay. |
| EXPERT: | Let's see what goes to the relay on the schematic... Is that with the turbo engine? Or without the turbo? |
| MECHANIC: | Without the turbo. |
| <checking> | |
| EXPERT: | Does it have a start-stop system? |
| MECHANIC: | It doesn't. |
| EXPERT: | There is supposed to be a power from the engine ECU to the leg 86 of the relay, but it goes through the box in the engine compartment. From the engine controller the control comes from pin number 29... |
| MECHANIC: | Yes, exactly. |
| EXPERT: | This wire goes to the box in the engine compartment... to the grey plug, to pin 29. And the question is, if you put power at pin 29, does the starter turn or not? |
| MECHANIC: | Yes, it fires, exactly, it turns normally. I have no 12 volts from the ignition, I don't get 12 volts when I turn the key, I lose current from pin 29 to the relay. |
| EXPERT: | Ok, so everything indicates that the engine controller is defective. |
| MECHANIC: | I understand, but why... because there are obviously no errors in the ECU. |
| EXPERT: | No, there aren't and it doesn't have to have any errors for the ECU to not deliver the voltage it receives to the output circuit. But there is also a chance that the ECU doesn't get one of the power supplies. |
| MECHANIC: | I checked all the voltages going to the ECU when cranking and nothing is happening, 12 volts are going to the controller. |
| EXPERT: | So, you have the answer. |
| MECHANIC: | It's just... why does it start when the car is parked in a warm garage? |
| EXPERT: | If there are cold solder joints in the controller then this will happen. Heat up the controller and see what happens. Take a heat gun, heat up the ECU and see if it runs. Even if the car stays in the cold. |
| MECHANIC: | I get it, ok. |
| EXPERT: | I suspect that the controller has a cold solder somewhere and it just doesn't give enough current to sustain the relay coil. |
| MECHANIC: | Yes, exactly, that's right, it doesn't give that 12 volt output from the controller to the relay to give good current to the starter so that the car would start normally. |
| EXPERT: | The problem will get worse and worse until the engine will not start at all. On short-circuit the relay works. Voltage should come out of the controller and it does, but with no load. If you put a light bulb, for example, I don't know what current the relay will draw, probably 100 to 200 mA, so if you took a 5 W bulb I suspect that it would not light upon that 29th pin. |
| MECHANIC: | Yeah, it won't light up, because even when I check with a test light when it starts, 12 volts shows up, on the test light it is ok. But when it doesn't fire, even a 1-2 W bulb won't light up. |
| EXPERT: | From what I see it will probably be hard to get such an ECU. If you have problems finding it, I think it's worth bringing to an auto electrician, even if only to determine the cause. Cold solders are relatively easy to check, because often a weak connection emits heat under load, so with a thermal imaging camera you can quickly locate where the problem is. |
| MECHANIC: | Ok, thanks, we'll see then. I must say I was maybe 99% prepared for this controller, I was just wondering why there was no error... because when I pulled out the starter relay then of course the error would appear, but I just thought that if there was a connection problem within the ECU then there would be an error, and there is no error. |
| EXPERT: | Before you buy another ECU just tell me exactly what you checked. Did you check connections in the wiring loom, pins of the controller and wiring to the control circuit? |
| MECHANIC: | Yes, exactly, such things always in the beginning - ECU, pins, plugs, everything was checked, so... yeah, here it is 100% - the pins on the relay as well as in the controller are tight and we also checked that nothing is happening to these pins - clean, nice, so... you should check that first of course. |
| EXPERT: | Because here you see the power amp in the ECU is voltage control - this rarely happens. Most ECUs are using ground controllers, it is easier and for the manufacturer it is cheaper. Actually, there are only advantages, if you control the ground. And if there is a voltage control then there are only problems. So... |
| MECHANIC: | Okay. I understand it all. |
| EXPERT: | Also remember about the immobiliser on the new computer. Because the old immobiliser still needs to be swapped over for sure. |
| MECHANIC: | Yes, yes, I know. Okay, thank you very much for your help, cheers, bye. |
| EXPERT: | Thanks, see you. |