Hi, long-time reader, first time poster. I've tried searching but not found a simple answer, if there is one apologies for double-tapping, please signpost!

I have a Mk2 1.8 Diesel estate, c.152k on the clock. I consider myself a reasonably competent drive-way mechanic but I'm struggling to understand this situation. I broke down last week with what seemed to be alternator failing - battery light, ABS, traction etc followed by complete shutdown. I recall a slight low-level hum or whirr linked to revs, I initially thought it was power steering pump.

Anyway, even several hours after recovery, the battery was absolutely roasting hot, reading c.6V. Seems to have eventually charged back to 12.4 and holding.

I got the alternator out eventually (curses to whomever designed that top bolt facing the wrong way) and the diodes seem to have over-heated and separated from the leads so thats toast. The alternator clutch is fine - spins one way, locks the other.

problem 1 - how do I tell what replacement alternator to get? the label is illegible and no other stampings to be seen. If it helps I have the heated front screen but no aftermarket stuff with high current draw. I think this means its a 120A, but cannot find a spec sheet or a handy label elsewhere in the car. I'm happy replacing just the bridge, but if its a rectifier, and considering this has probably the full 150k on the clock (owned since 16k) its probably time to consign it to electrical heaven.

 

The concern I have now, is that when I connect the battery via cables direct to the terminal clamps, the voltage drop is c1.6V, and no power to the car, instrument cluster or ignition. When I connect negative across the engine to another earth, I get 12.4V, and the car powers up.

The alternator is still off, cables are not shorting, and there is open circuit on multimeter. Fault code is P0A09, (DC/DC converter low), which appears to be more linked to hybrid/electrical cars, or possibly indicating a PCM fault. I'm stumped what to make of this. Maybe a loom fault, but visual check/continuity check seems to be ok.

Problem 2 - could this also be a damaged starter, damaged loom or ECU? I recently had the 'sack of spanners' failed DMF and had that replaced plus clutch, so worried about the starter, but had zero issues with starting until the electrical failure, about 4 weeks after DMF replacement. I would appreciate any other tests to run, or things to look at before I end up throwing good money after bad.

 

Thanks all in advance!

Hmm, a bit quiet on the response side so I'll update - found the right one thanks to a great chap at the startermotorsalternator company in Devon, who have a bunch of these Denso 150A types going cheap. Everything went back together, battery tested fine at a local fixer, and no codes showing after about 20mins run. Battery then died completely overnight but probably too cold and is on its last legs after recent over-voltage. More money at Halfrauds then.

Not sure if I need to get into the PCM and change the alternator type or size from ?? to 150A but good excuse to blow the dust off the cobwebs on FORScan. Does anyone have advice on that? I've seen some mixed responses to similar questions but from some time ago.

Thanks in advance if anyone is able to respond?

On 1/26/2025 at 1:19 PM, FordPadawan said:

failed DMF and had that replaced plus clutch, so worried about the starter, but had zero issues with starting until the electrical failure, about 4 weeks after DMF replacement. I would appreciate any other tests to run, or things to look at before I end up throwing good money after bad.

Firstly I think its time for a new alternator. Just put your registration number in any of the big parts suppliers and it will list alternators for your car. I tend to use Autodoc, but you could use someone like GSF.

The fact that the battery has been discharged as low as 6V means it will be permanently degraded now and should really be replaced.

Lastly but quite probably the most important. It sounds like the main earth lead between the gearbox and chassis is either damaged or missing.

On 1/26/2025 at 1:19 PM, FordPadawan said:

Hi, long-time reader, first time poster. I've tried searching but not found a simple answer, if there is one apologies for double-tapping, please signpost!

I have a Mk2 1.8 Diesel estate, c.152k on the clock. I consider myself a reasonably competent drive-way mechanic but I'm struggling to understand this situation. I broke down last week with what seemed to be alternator failing - battery light, ABS, traction etc followed by complete shutdown. I recall a slight low-level hum or whirr linked to revs, I initially thought it was power steering pump.

Anyway, even several hours after recovery, the battery was absolutely roasting hot, reading c.6V. Seems to have eventually charged back to 12.4 and holding.

I got the alternator out eventually (curses to whomever designed that top bolt facing the wrong way) and the diodes seem to have over-heated and separated from the leads so thats toast. The alternator clutch is fine - spins one way, locks the other.

problem 1 - how do I tell what replacement alternator to get? the label is illegible and no other stampings to be seen. If it helps I have the heated front screen but no aftermarket stuff with high current draw. I think this means its a 120A, but cannot find a spec sheet or a handy label elsewhere in the car. I'm happy replacing just the bridge, but if its a rectifier, and considering this has probably the full 150k on the clock (owned since 16k) its probably time to consign it to electrical heaven.

 

The concern I have now, is that when I connect the battery via cables direct to the terminal clamps, the voltage drop is c1.6V, and no power to the car, instrument cluster or ignition. When I connect negative across the engine to another earth, I get 12.4V, and the car powers up.

The alternator is still off, cables are not shorting, and there is open circuit on multimeter. Fault code is P0A09, (DC/DC converter low), which appears to be more linked to hybrid/electrical cars, or possibly indicating a PCM fault. I'm stumped what to make of this. Maybe a loom fault, but visual check/continuity check seems to be ok.

Problem 2 - could this also be a damaged starter, damaged loom or ECU? I recently had the 'sack of spanners' failed DMF and had that replaced plus clutch, so worried about the starter, but had zero issues with starting until the electrical failure, about 4 weeks after DMF replacement. I would appreciate any other tests to run, or things to look at before I end up throwing good money after bad.

 

Thanks all in advance!

The starter motor is probably full of metal dust from the failed DMF. 
My MK 1.5 TDCI struggled to start not long after having had the DMF replaced. 

On 2/4/2025 at 11:24 PM, unofix said:

Firstly I think its time for a new alternator. Just put your registration number in any of the big parts suppliers and it will list alternators for your car. I tend to use Autodoc, but you could use someone like GSF.

The fact that the battery has been discharged as low as 6V means it will be permanently degraded now and should really be replaced.

Lastly but quite probably the most important. It sounds like the main earth lead between the gearbox and chassis is either damaged or missing.

unofix, great call thanks, I cant see any obvious wire on the top mount under the airbox or battery tray, but I cant see any obvious place it would have earthed to - no disturbed dirt or other grounding points. I'll get under it this weekend and have a good look around.

I have used Autodoc before but they have replaced items with own-brand without checking with me first so wasnt happy, plus it takes ages to get the parts, I was in a rush. Not ideal but hey. When they got it right it was good parts for good price to be fair.

Battery seems to be holding but its not new and probably due for replacement. I'll see how long it holds in this cold weather but so far so good.

On 2/5/2025 at 9:38 AM, Drive a Focus. said:

The starter motor is probably full of metal dust from the failed DMF. 
My MK 1.5 TDCI struggled to start not long after having had the DMF replaced. 

Hi Michael, thanks, yes I was worried about this too so the starter came off and had a good test as well. No metal shavings or dust, no sparks or sticking so hopefully all good after a gentle clean-up.

@FordPadawan did you get this fixed? I had a recent alternator failure on same car as yours. I think they're all 150A alternators on that model. I would have changed the battery straight off, £90 and 5 min job, that old one must be ruined. I was unlucky enough to get a faulty reman alternator so had to change the alternator twice, I posted at length about my pain!

I had a similar experience with a Ford remanufactured alternator failing after a month of use. Not helped by an alternator ‘specialist’ testing it and declaring it was ok leading me to refit it and start going down other blind alleys to find the fault 🙄

All this in the middle of heavy winter snowfall and covid made it worse!

On 2/15/2025 at 10:13 PM, Jim_Cambridge said:

@FordPadawan did you get this fixed? I had a recent alternator failure on same car as yours. I think they're all 150A alternators on that model. I would have changed the battery straight off, £90 and 5 min job, that old one must be ruined. I was unlucky enough to get a faulty reman alternator so had to change the alternator twice, I posted at length about my pain!

@Jim_CambridgeYes it all seems to have worked out (reaches to touch wood!) even still have the same battery which probably got variously roasted, overcharged then over-drained but holding in there, both for short and long journeys. I got a good quality battery charger with repair function on it almost straight away and seems to have saved it. Time will tell.

Biggest pain TBH was the alternator mount upper bolt which some design clown put facing the wrong way needing fingers of an octopus, strength of Garth and a mini 10mm spanner to turn. FORSCAN showed 150A alt on the records so think you must be right.

BTW thanks for the detail in your post, I did have a good read at the time and hence went straight for a 'new' not refurb alt, but sadly only had me to do the change rather than 2 people. Lots of what I now call "Garage-Fit" (as opposed to Cross-Fit) of lunges, pressups, shuffles and twist-situps with items of various weights in hand between getting under the car and then under the bonnet.