ECU faulty

[StevenMcGowan72]

Hi folks, my 2003 zt-t cdti mk1 broke down on me some time ago, mechanic has been working on it in his spare time, replaced the rear fuel pump, now my ecu is reading a low voltage, car wont start without using easy start...so looks like it's the ecu that needs repaired or replaced, need help. Thanks all.

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[Lovel]

Originally Posted by StevenMcGowan72

Hi folks, my 2003 zt-t cdti mk1 broke down on me some time ago, mechanic has been working on it in his spare time, replaced the rear fuel pump, now my ecu is reading a low voltage, car wont start without using easy start...so looks like it's the ecu that needs repaired or replaced, need help. Thanks all.

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Before you jump to conclusions on the ECU you should do more fault finding. How much pressure are you getting from the underbonnet pump? If you are reading ECU voltage then can’t you see underbonnet fuel pump pressure with the diagnostic tool you are using? Define low voltage? Has the ECU been immersed in water at some point?

Requires more than 1.2 Bar before the ECU will allow starting.

[StevenMcGowan72]

Originally Posted by Lovel

Before you jump to conclusions on the ECU you should do more fault finding. How much pressure are you getting from the underbonnet pump? If you are reading ECU voltage then can’t you see underbonnet fuel pump pressure with the diagnostic tool you are using? Define low voltage? Has the ECU been immersed in water at some point?

Requires more than 1.2 Bar before the ECU will allow starting.

I've sent an image showing the voltages from toaf

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[StevenMcGowan72]

Originally Posted by StevenMcGowan72

I've sent an image showing the voltages from toaf

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And my prenum drain was full of water.

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[Lovel]

So is it 10.32v bit? I don’t use TOAF I use T4. Cant you see the Low fuel pressure Side with TOAF?

Battery voltage ?

[StevenMcGowan72]

Originally Posted by Lovel

So is it 10.32v bit? I don’t use TOAF I use T4. Cant you see the Low fuel pressure Side with TOAF?

Battery voltage ?

I have no idea, the guy that sent the image said it was defo the ecu as it wasnt reading the fuel pressure properly, said all other electrics were fine, rear pump not showing any signs or working, as no sound coming from it.

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[Lovel]

Check relay engine bay R4.

Terminals 86 + 87 should have 12v

Check continuity from relay terminal 30 to pin1 at ecm yell/red CO603-1 & CO603-1

Check continuity from relay terminal 85 to pin9 at ecm, black/pink CO603-9

Connector CO603 has 9 pins at the ECM.

[Lovel]

Check fuel pump relay inside passenger compartment, it’s a smaller type of mini relay.

Check Continuity
CO730-4 black/purple To C0331-10 at Ecm 40 pin connector ( I have seen this wire fail in past, and ended up running jumper wire in place)

Check for voltage
CO730-8 purple/green at mini relay Power from fuse 20 in passenger Cmpt
CO730-6 brown/light green at min relay. Power from fuse 20 but looped through inertia switch

[Yorkshire GOC]

You can get a picture of how the ECU is managing the fuel mix - using a bog standard OBD tool but i suppose TOAF does this but just in case you have not - look at the data stream readings for Short Fuel Trim (SHRTFT) and Long Fuel trim (LONGFT- both should be in the range +10% and -10% - ideally around +5% . SHRTFT will fluctuate as the ECU compensates the fuel mix while the LONGFT should be stable. I recently ran this test to check my fuel pumps operation.


Higher/Positive percentages in the fuel trim means the engine computer is trying to compensate for a lean condition in the motor by enriching the mixture. This means the vehicle might have problems with the fuel system, injectors, oxygen sensors, or mass air flow sensor. This can also mean vacuum leaks in the system.


On the other hand, a Negative/Lower fuel trim means the CPU is attempting to switch the fuel mixture to lean to recompense a rich mixture. From this reading, it could possibly mean excessive pressure or leaking fuel injectors, a ruptured fuel pressure diaphragm, or a faulty EVAP system. If the STFT or LTFT readings are exceeding 10%, this signifies a problem in the fuel system.

The fuel trim should be checked During engine idle at 1,500 rpm; and at 2,500 rpm
It is important to check the fuel trim in all the required operating stages. As an example, if the LTFT is at 20% during idle but adjusts correctly to 5% at 1,500 and 2,500 rpm, the focus should be on certain problems that cause the lean engine condition at idling speed. But if the LTFT is at 20% at all stages, this could mean a problem with the fuel supply such as a bad fuel pump.

However as your ECU has been for a swim i suspect your ECU is goosed - some folk try to dry them out - pack in rice or leave in an airing cupboard for 48 hours and keep your fingers crossed -worth a try.

[Lovel]

Hope these help?

Take your ECM out and check inside it for water damage. Be careful to ensure that when removing the body of the ECM does not touch any of the battery terminals. Stating the obvious but if the battery cover is not present you really do risk frying it.

If it is you ECM has indeed been swimming, and If no trader can help with a replacement ECM then I might be able to help out.

Right it now time to get back to my shed and not get stuck inside on such a beautiful day.