Peugeot 406 HDI poor fuel economy - LukeMH
My 1999 406 HDI 90 is suffering poor fuel economy. I am on 101,000 miles.

When the car was new I remember getting 55mpg from a tank on occasions. For the last year I've been getting 45mpg combined.

On my last few tanks of fuel I'm getting 39mpg and on this most recent tank I have got 37mpg. The thing that has really flagged this up wtih me is that I'm off work and so the only driving I have been doing over xmas is motorway driving at 50-60mph to and from relatives, also the air con is off (and it would normally be on but its gone noisey so i have stopped using it)

At 50-60mph with the aircon off I would expect 55mpg

Any suggestions on whats a likely cause?

My local mechanic is great, but he's one that likes to keep costs as low as possible (which is great in one way) but he doesn't tend to like checking or replacing anything that isn't actually *broken*, or that I specifically instruct him to do

Any help greatly apreciated



PS thanks for all the useful info I have picked up on here. My car ticks up to 3000rpm so thanks to this forum I now know I *must* replace my timing belt pulley on my next visit to the mechanic.

I also know how to fix the stupid "brake fluid low" warning too
Peugeot 406 HDI poor fuel economy - CG
I ran a 2000 X-plate 406 HDi 90 (Estate) from new to 96,000 miles. My best was 52 (computer) 49 (brim-to-brim), with sensible driving. I never achieved 55 overall, even at modest speeds on long motorway journeys. The consumption did seem to rise a little as it got older, but only by 1-2 mpg. Thoughts - fuel filter needs changing? What brand of fuel are you using - Shell and BP appear to be rated the best. Tried using Millers Diesel Plus? I found that this paid for itself with slightly better mpg, and the engine was smoother and quieter (not that these are normally noisy). A brake binding perhaps?

Peugeot 406 HDI poor fuel economy - Mr Fish
There's a known problem with older Xantias where corrosion builds up around the rear brake callipers gradually pushing them onto the disc. Don't know if the 406 has the same arrangement but it wouldn't surprise me. Anytime I checked my xantia there was slight binding but it seemed ok. However when i finally got round to fixing it, the difference in MPG was surprising. I think the binding gets worse as things heat up.
Peugeot 406 HDI poor fuel economy - LukeMH
Mines a saloon hence why you could get 52 and i could get 55, as the estate does make a difference to the economy. I am measuring brim to brim as i dont have the trip computer.

Thanks both of you I will check the brakes, but I suspect something more sinister, 37mpg for motorway is REALLY bad.
Peugeot 406 HDI poor fuel economy - LukeMH
Oh forgot to say I'm using tesco fuel and always have done. It probably is low quality being cheap, but then its always fresh as there are queues at the tesco garage 24/7

I will chuck some injector cleaner in when its empty and fill up with BP or simular and see if that helps

Peugeot 406 HDI poor fuel economy - Mondaywoe
Air filter clean? Exhaust system clear? (Possibly coked up or a baffle collapsed in the silencer?)Brakes binding? Tyres underinflated? Has the timing belt been changed recently - possibly a tooth out?.On the other hand it might just be wear and tear beginning to take its toll on engine components generally.Consumption can also vary according to season.

Peugeot 406 HDI poor fuel economy - CG
My 406 HDi 90 had drums on the rear, and if Luke's are the same then the caliper problem shouldn't be the cause in his case.
Peugeot 406 HDI poor fuel economy - LukeMH
Air filter is clean, I change it as soon as it starts to look dirty (10-12k) not 24k like the stupid peugeot service interval specifies.

The exhaust from the backbox up to the cat is 6months old so I don't suspect its that really.

The rear brakes are disc over drum (why?? my 1996 406 had just discs on the rear) but I will get my mechanic to check the brakes out for binding on next service.

I suspect the cam pulley needs replacing, so thats an item for next service. When that gets replaced I'll know it is lined up correctly.

Yes it's done just over 100,000 miles, but whenever it is in the garage the mechanic has commented that its running beautifully. It's reasonably smooth, pulls strong and smokes less then most new diesels (recent mot showed smoke to be very low for its age) , it doesn't burn a single drop of oil between services. It has been looked after and has been serviced at twice the recommended intervals (oil at 6k and full service at 12k - instead of peugeots 12k-24k) soooo ..... I will be very angry if 37mpg is all I can expect from it now, but then again it is a Peugeot, so It was probably designed to self destruct at 100k. Everyone knows how good the old XUD was but the HDI doesnt seem to be proving anywhere near as reliable.

No smoke should mean that its getting plenty of air, and the injectors should be clean, but as mentioned before, I'll chuck some injector cleaner in next fill up, and some good quality fuel. Is there a league table somewhere for test results of the latest diesels?

Thanks for everyones input so far. I will keep posted if I find a solution, I really have to sort this as I can't afford to be getting petrol fuel economy, otherwise i might as well sell and buy a cheaper petrol car.
Peugeot 406 HDI poor fuel economy - DavidHM
If it's any consolation I'm having much the same problem - no obvious symptoms but consumption dropping in 6 months from 44 to 35 mpg - from my 1996 406 1.9 with 107k.

I'm liking the brake binding theory, assuming that it doesn't manifest itself.

It's due for a service in a couple of weeks so I'll ask about it then.
Peugeot 406 HDI poor fuel economy - CG
A binding brake should be quite easy to detect - after a good run immediately feel all 4 wheels. The fronts will probably feel warmer as they do most of the braking. What you are looking for is one wheel that is noticeably warmer than its oppo on the same axle.
Peugeot 406 HDI poor fuel economy - CG
Sorry if this sounded like teaching your grandmother to suck eggs - not intended!
Peugeot 406 HDI poor fuel economy - LukeMH
Well, my brakes are not binding.

I did a fill up on BP ultimate diesel and also waited for the tank to get near empty, filled it up with a full bottle of injecctor cleaner and drove down the motorway in 3rd gear. Lots of grey smoke came out for a few seconds then it ran clear.

Unfortunatly this has done nothing for my fuel economy as I am still getting no more then 39mpg :(

Oh and I am not alone, I've seen other reports/messages/posts of people getting 40mpg or less from peugeot 406's but I see no solutions to anyone elses complaints.

On a related topic, one of the pool cars at work is a Renault Laguna II dci 120 (1 year old) and on a 100 mile motorway run at 60-70mph (in 6th gear) the onboard computer read out 41.9mpg for the journey when this car should like mine be getting near 60mpg on the motorway.

Another one of works cars is a VW passat PD100 on a simular journey I have seen that car reporting 56mpg

Looks like the solution is to scrap my 406 and buy a VW/Audi/Skoda/Seat with one of those lovely PD engines
Peugeot 406 HDI poor fuel economy - Mike M
Just a thought, Luke, but have you got a EGR problem? If the valve is not seating correctly, you could be feeding exhaust gasses back into the inlet manifold at all speeds making the fuel burn less efficient. Not sure how to check it other than removing it for a physical examination. It's at the back of the engine on the left hand side - see the Haynes manual page 4D.3 for details. Seems quite easy, but you may need a new gasket. Just for comparison, my 406 HDi(90) has done 100K and still returns over 50mpg, so don't give up.
Peugeot 406 HDI poor fuel economy - dieselnut
To save removing the EGR valve. Take off the vacuum pipe to the valve. Start the engine from cold & carefully touch the pipe conecting the EGR to the exhaust near to the EGR valve. If it starts to get hot straight away you will know exhaust gas is getting through the valve when it shouldn't.
The first thing I do to any diesel car I get is disconnect this permanently. They seem to cause a lot of niggly problems that are difficult to determine yet give little benefit IMHO.
Peugeot 406 HDI poor fuel economy - Fetch

I know that this post is very old but needless to say that it is because of this I am here. I too was suffering the same issue. Great mileage 55mpg was the norm and easily going from Calasis to the South of France on a full tank. Bliss.... but then it all changed and I was only getting half that at best.

I went through the list:

1. Tyres - Under inflated slightly but pumped them up.

2. Checked the tracking - Toe-ing in on the left and slightly out on the right. Not by huge amounts but enough. Needless to say it needed to be done as the full suspension had been replaced (struts, springs, bushes and ball joint).

3. Filters - needed a service any way so they were changed but they have been annually anyway.

4. Clogged exhaust/inlet - no to both. A new exhaust was fitted so I could discount that part.

5. Brake binding! Now there is where it gets interesting especially on the rear!

Jacking up the car, taking all the usual precautions, and spinning the back wheel would normally free wheel with the slightest bit of rubbing if your brake shoes were ok. But there is where the problem was as the rubbing was not the brake shoes after all. Upon removing the disc I noticed that there was a fair bit of rust build up on the inner edge with a slight shine to it. Upon inspecting the back plate of the said side there were two very distinctive rubbing marks! BINGO! To top that the opposite side was the same too.

I have attached a link to the video I made so you can see what I am refering too but included in there is a good instruction guide to how to change the brakes yourselves!

Peugeot 406 HDI poor fuel economy - Peter.N.

At a steady 50-60mph I get 60 mpg+ from my 110hp so I would have thought the 90hp should do at least as well. Is your engine temperature running at normal. Do you have a fuel computer if not are you checking it by brimming the tank?

Peugeot 406 HDI poor fuel economy - Peter.N.

I know this is an old post but as I made the last one I thought you might be interested in what has just happened to me.

My old 406 estate was doing 50-60 mpg pretty well all the time, it has covered 246,000 miles and still drives beautifully, I have just bought another one with only 181k on it it and judging by the pile of receips that came with it every time its gone into a garage its had something new, it sounds and drives like a new car but is only doing 45 mpg, now I have the same dilemma.

The EGR valve is something that hadn't crossed my mind so thank you for the suggestion.

Peugeot 406 HDI poor fuel economy - Peter.N.

I have just rediscovered this thread so thought I would tell you what I found, after driving all the way to the north of Scotland I found my n/s front brake caliper was seized, not rusty or corroded just seized, after a few miles it would release, it wasn't until it started squealing I found it, having replaced it I am now getting another 6-7 mpg.

Peugeot 406 HDI poor fuel economy - Andrew-T

Peter - wouldn't that generate a lot of heat ?

Peugeot 406 HDI poor fuel economy - Peter.N.

Yes it was generating a lot of heat but as the brake was releasing after a few miles it wasn't overly hot, I expect if I had checked it before it released it would have been, but strangly enough couldn't smell anything. You could certainly feel that the wheel was hot when you stopped.


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