# Limp home mode kicking in on motorway, what should I do? **URL:** \ **Category:** Factual Questions\ **Created:** [June 25, 2013, 5:16pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889 "2013-06-25T17:16:25Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Mr\_Shine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mr_shine/32/464_2.png) [@Mr\_Shine](https://boards.straightdope.com/u/Mr_Shine)\ **Post date:** [June 25, 2013, 5:16pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/1 "2013-06-25T17:16:25Z")
I live in the UK. Whilst driving about, my car went into limp-home mode, putting the engine light on the dash and restricting it to 20mph. When I parked and started the engine again it went back to normal. I’ve had my garage look at it but with the engine light no longer there it’s not giving any error messages and they don’t know where to start looking for a fault. I’m not sure what I should do though if it kicks in again, this time on a motorway. Should I drive at 20mph in the left lane with hazards, drive at 20mph on the hard shoulder with hazards, or do I have to call out a breakdown service (the option I really don’t want to do)? ---
**Author:** ![Kenm](https://avatars.discourse-cdn.com/v4/letter/k/bc79bd/32.png) [@Kenm](https://boards.straightdope.com/u/Kenm)\ **Post date:** [June 25, 2013, 5:20pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/2 "2013-06-25T17:20:59Z")
Cars’ computers store the fault numbers. It should be there if you plug in the reader. [**This link**](https://www.google.co.uk/search?as_q=car+computer+fault+store&as_epq=&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=&as_occt=any&safe=images&tbs=&as_filetype=&as_rights=) goes to a bunch of others. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [June 25, 2013, 5:34pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/3 "2013-06-25T17:34:53Z")
I am fairly sure that the ‘official’ advice would be to find a wide bit of hard shoulder (ie not under or on a bridge), pull over as far as you can, get out of the car and retreat to the verge. Then you should phone your recovery service. In practice I think you should weigh up the circumstances. Driving in a ‘live’ lane at 20 mph is a definite no no. Driving any great distance on the hard shoulder is inadvisable and can be dangerous but if there was a MSA or an exit within a couple of miles I would risk it. Remember that MSAs have a back gate so you can get out onto the ordinary road system and once there you can decide whether to drive home or to a garage. In the immediate future - get those codes checked because it will surely happen again. ---
**Author:** ![TruCelt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/trucelt/32/523_2.png) [@TruCelt](https://boards.straightdope.com/u/TruCelt)\ **Post date:** [June 25, 2013, 5:55pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/4 "2013-06-25T17:55:24Z")
It sounds like a drop in oil pressure-in which case continuing to drive can cause major damage. Of course it might not be-in which case it wouldn’t. Glad I could help. 😉 ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [June 25, 2013, 6:03pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/5 "2013-06-25T18:03:16Z")
> [@Kenm](#): > > Cars’ computers store the fault numbers. It should be there if you plug in the reader. [**This link**](https://www.google.co.uk/search?as_q=car+computer+fault+store&as_epq=&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=&as_occt=any&safe=images&tbs=&as_filetype=&as_rights=) goes to a bunch of others. No, if the check engine or service engine light turned itself off, as the OP says, there will no longer be a code to read. They are usually only stored while the light is lit. The OP could buy an OBD II data reader of his own, they aren’t very expensive for a basic model, and then he can read the code himself next time the condition occurs. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [June 25, 2013, 6:23pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/6 "2013-06-25T18:23:07Z")
> [@Dallas\_Jones](#): > > No, if the check engine or service engine light turned itself off, as the OP says, there will no longer be a code to read. They are usually only stored while the light is lit. On all the OBDII cars I’m familiar with, if the fault fixes itself (or you fix it and don’t clear it) the light goes out but the code is still stored in the memory until there have been a certain number of of drive cycles without the problem reoccuring. Maybe that’s different on UK models, but I don’t see why it would be. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [June 25, 2013, 7:17pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/7 "2013-06-25T19:17:23Z")
> [@GreasyJack](#): > > On all the OBDII cars I’m familiar with, if the fault fixes itself (or you fix it and don’t clear it) the light goes out but the code is still stored in the memory until there have been a certain number of of drive cycles without the problem reoccuring. Maybe that’s different on UK models, but I don’t see why it would be. Agreed. It doesn’t make sense to me that there’s no code in the memory, assuming it is indeed an OBDII system. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [June 25, 2013, 7:38pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/8 "2013-06-25T19:38:04Z")
as always, it would be very helpful if you provided the make, model, and year of the car. Does it have electronic throttle control? did any other warning lights come on? ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [June 25, 2013, 8:07pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/9 "2013-06-25T20:07:09Z")
Possibly it set a transmission code and the shop only looked for engine codes. ---
**Author:** ![Mr\_Shine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mr_shine/32/464_2.png) [@Mr\_Shine](https://boards.straightdope.com/u/Mr_Shine)\ **Post date:** [June 25, 2013, 8:54pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/10 "2013-06-25T20:54:23Z")
Apologies, my summary wasn’t accurate, it was abbreviated. I didn’t actually get to the garage, I called them and the guy I spoke to told me to bring it in if it happened again, and he certainly suggested that he couldn’t do anything if I bought it in whilst the light was off, but nobody did actually look at it. I simplified the story down as the question in the OP was what I was interested in, I considered the full story superfluous and I did not realise the difference it made. I’ll call in the morning to query that, thanks. ---
**Author:** ![Mr\_Shine](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mr_shine/32/464_2.png) [@Mr\_Shine](https://boards.straightdope.com/u/Mr_Shine)\ **Post date:** [June 25, 2013, 9:02pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/11 "2013-06-25T21:02:09Z")
Oh, for anybody who is interested, the car is a 2004 Skoda Fabia, but again this wasn’t supposed to be a car question, more a “what to do if this happens?” question. Thanks for your interest though. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [June 25, 2013, 9:09pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/12 "2013-06-25T21:09:55Z")
> [@Mr\_Shine](#): > > Should I … drive at 20mph on the hard shoulder with hazards Don’t do this. Either stop by one of the phones and advise the emergency services and then the recovery service if appropriate, or drive in the left-hand lane and exit the motorway ASAP. See the Highway Code [here](https://www.gov.uk/breakdowns-and-incidents-274-to-287/additional-rules-for-motorways-275-to-278). ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [June 25, 2013, 10:59pm UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/13 "2013-06-25T22:59:38Z")
> [@Mr\_Shine](#): > > Oh, for anybody who is interested, the car is a 2004 Skoda Fabia, but again this wasn’t supposed to be a car question, more a “what to do if this happens?” question. Thanks for your interest though. well, conventional wisdom (at least with US OBD-II systems) is a steady check-engine light means any fault that could cause the engine’s emissions to exceed the standards it was certified to, and may or may not involve driveability problems. A \*\*flashing \*\* check engine light means you should pull off the road safely and shut the car off as soon as possible; typically this means a repeated misfire which could cause damage to the catalyst(s.) Since you were experiencing a driveability problem, stopping the car to assess the situation was prudent. If you’re on a motorway with limited options for safely not obstructing traffic, and the fault keeps reoccurring, then honestly the best option is to pull aside to the shoulder, stop, and call for a tow. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [June 26, 2013, 1:13am UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/14 "2013-06-26T01:13:13Z")
It sounds like the experience people have with diesel vehicles fitted with particulate filters. The filter is designed to collect and burn (oxidise) particles of soot… [http://www.skoda-auto.com/GBR/Documents/19246\_Skoda\_DPF\_Leaflet\_v7.pdf](http://www.skoda-auto.com/GBR/Documents/19246_Skoda_DPF_Leaflet_v7.pdf) Here is the procedures for ensuring the filter is cleaned out. [http://wiki.ross-tech.com/wiki/index.php/Diesel\_Particle\_Filter\_Emergency\_Regeneration](http://wiki.ross-tech.com/wiki/index.php/Diesel_Particle_Filter_Emergency_Regeneration) It could also be clogging of other filters and sensors too though… which may mean its unreliable as many won’t fix themselves. (can also just be a freak drop of water on the electrics that has since dried away… ) ---
**Author:** ![rogerbox](https://avatars.discourse-cdn.com/v4/letter/r/76d3ee/32.png) [@rogerbox](https://boards.straightdope.com/u/rogerbox)\ **Post date:** [June 26, 2013, 2:25am UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/15 "2013-06-26T02:25:02Z")
I’m suspicious that your car doesn’t store error codes and your mechanics cannot look up an error code that just happened if the light is not longer on, especially since your car is relatively new… I would try another shop. :dubious: ---
**Author:** ![Grrr](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/grrr/32/146_2.png) [@Grrr](https://boards.straightdope.com/u/Grrr)\ **Post date:** [June 26, 2013, 8:29am UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/16 "2013-06-26T08:29:50Z")
Is LHM a UK thing? Because I’ve never heard of that here before. Nor am I aware of any cars that have it here. (US) ---
**Author:** ![Ximenean](https://avatars.discourse-cdn.com/v4/letter/x/aca169/32.png) [@Ximenean](https://boards.straightdope.com/u/Ximenean)\ **Post date:** [June 26, 2013, 10:03am UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/17 "2013-06-26T10:03:20Z")
It’s common on diesel engines, at least. I would guess that the OP has a VW Group TDI diesel. I understand diesels are less common in the US. ---
**Author:** ![Aspidistra](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aspidistra/32/3894_2.png) [@Aspidistra](https://boards.straightdope.com/u/Aspidistra)\ **Post date:** [June 26, 2013, 10:15am UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/18 "2013-06-26T10:15:01Z")
> [@Ximenean](#): > > It’s common on diesel engines, at least. I would guess that the OP has a VW Group TDI diesel. I understand diesels are less common in the US. VW?? Is there any potential connection to [this](http://news.drive.com.au/drive/motor-news/death-prompts-vw-owners-to-speak-out-20130530-2nexi.html) then? ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [June 26, 2013, 10:38am UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/19 "2013-06-26T10:38:11Z")
If it is a diesel-engined car with a DPF, then the usual cause is driving about town too slowly, which allows the DPF to get clogged. The simple solution is to thrash it on the motorway once a week. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [June 26, 2013, 10:43am UTC](https://boards.straightdope.com/t/limp-home-mode-kicking-in-on-motorway-what-should-i-do/661889/20 "2013-06-26T10:43:03Z")
> [@Shakes](#): > > Is LHM a UK thing? Because I’ve never heard of that here before. Nor am I aware of any cars that have it here. (US) any car with electronic throttle control (meaning, pretty much any car on the market) has a limp home mode if the PCM detects a fault in the throttle motor or position sensor circuits. also, many electronically controlled automatic transmissions have one as well, they’ll stay in one gear (usually 2nd or 3rd) to prevent faulting controls from burning up the clutches.