MOT advisory explained
“Undertray not fully secure”
The plastic panel under the engine has lost a clip or two and is hanging at one corner. It is the least consequential advisory on the certificate, it fails at the next test less often than almost anything else, and the fix is a bag of clips. It is still worth ten minutes, because a tray that drops on the motorway is not nothing.
Most modern cars have a plastic tray bolted or clipped under the engine bay to smooth the airflow, keep spray off the engine and cut noise. The tester found it loose, cracked, or short of a fixing, but still attached. It does not affect how the car drives or stops.
0.6% fail on an undertray at the next test, among the lowest figures we have measured, and only 8.6% are advised again. Most are refixed at the next service, if only because the garage has to take it off to change the oil.
A handful of the correct push-fit clips or bolts. If the tray itself has cracked at the fixing holes, a replacement tray is priced by model.
The same wording covers “exhaust heat shield” and “heat shield”. A loose exhaust heat shield rattles and, unlike a tray, sits against something hot. If the note says heat shield, have it refixed rather than removed: it is there to keep exhaust heat off the floor and the fuel lines.
An “undertray not fully secure” advisory means the plastic panel under the engine bay, or a piece of sound deadening or heat shield, has lost some of its fixings or is damaged but is still attached, so the car passes. The fix is usually replacement clips, costing £10–£40. According to DVSA MOT data analysed by PriceMyRepair, only 0.6% of 83,373 such advisories followed to the next test failed on an undertray, and 8.6% were advised again.
What the tray is for and how it comes loose
Three jobs. The undertray keeps road spray and stones off the belts, alternator and wiring underneath the engine, it tidies the airflow under the car for fuel economy, and on many cars it carries sound deadening to keep engine noise out of the cabin. None of these is a safety function, which is why the MOT treats it lightly.
How it gets damaged. “damaged” is the most common note by a distance. Speed humps, steep driveways and kerbs catch the leading edge. Push-fit clips break when a garage removes the tray for a service and the old clips are refitted or not refitted at all. “missing” appears too, for the cases where the tray has gone completely and the tester is noting what is left.
What else is recorded here. The second wording covers sound deadening and heat shields. “exhaust heat shield” and “wheel arch liner” are the two other things testers name. A loose heat shield is the noisier and more useful of the group to fix.
Will it fail next year?
Two wordings, recorded 190,434 times between them, with 83,373 followed to the same vehicle’s next MOT.
| What happened at the next test | Share |
|---|---|
| Failed on the same component | 0.6% |
| Same advisory recorded again | 8.6% |
According to DVSA MOT data analysed by PriceMyRepair: 83,373 advisories followed to the same vehicle’s next test. Rows can overlap.
Fewer than one in a hundred fail next time, and the failure is a tray or shield that is about to fall off or is dragging. Compare a defective exhaust mounting at 5.5% or a noisy exhaust at 0.9%, both in the same section of the test.
The repeat rate is among the lowest for any advisory. The tray comes off at every oil change, and a garage that has it in its hands tends to put it back properly.
| Advisory wording | Fails on same part | Advised again | Followed |
|---|---|---|---|
| Exhaust mounting defective | 5.5% | 23.3% | 1,459,563 |
| Registration plate deteriorated | 3.7% | 40.1% | 4,283,862 |
| Bumper mountings corroded | 3.0% | 13.0% | 54,443 |
| Engine mounting damaged | 2.2% | 13.6% | 101,134 |
| Brake pedal wearing smooth | 1.4% | 26.2% | 320,684 |
| Exhaust noisy | 0.9% | 39.7% | 382,681 |
| Undertray not fully secure | 0.6% | 8.6% | 83,373 |
Uncommon at every age, from 0.3 per 1,000 tests at 3–4 years to 0.7 in the teens. There are too few cases past twenty years to report, because most cars of that age were built without a tray. The failure rate never rises above one in a hundred.
| Age of car | Per 1,000 tests | Fails on same part | Followed |
|---|---|---|---|
| 3–4 years | 0.3 | 0.3% | 7,814 |
| 5–6 years | 0.4 | 0.2% | 10,231 |
| 7–9 years | 0.6 | 0.6% | 19,896 |
| 10–12 years | 0.7 | 0.7% | 20,198 |
| 13–15 years | 0.8 | 0.8% | 14,178 |
| 16–19 years | 0.7 | 0.7% | 6,894 |
Most trays are held by a mix of push-fit plastic clips and self-tapping screws around the edge. Buy the clips for your car by registration, because sizes vary. A cracked fixing hole can be bridged with a large washer under the bolt head.
If the tray is beyond saving, a pattern replacement for a common car is inexpensive and the old tray comes off in minutes. Some owners on rough roads leave it off; that costs a little fuel economy and puts the belts in the spray, and on some cars the tray is also part of the engine cooling airflow.
Never zip-tie a tray to anything that moves or gets hot. The steering rack, driveshafts and exhaust are all directly above it.
Exact wording on your certificate
Two advisories for a loose tray or shield. The failure is one that is likely to come off.
| Line on the certificate | Result | Code |
|---|---|---|
| Undertray not fully secure | Advisory — pass | 8.1.1 (b) (i) |
| Sound deadening material not fully secure | Advisory — pass | 8.1.1 (b) (i) |
| Undertray insecure and likely to become detached | Major — fail | 8.1.1 (b) (ii) |
Half the entries have no position and most of the rest say front, since the engine undertray is the front one. The few marked rear are usually the heat shield above the rear silencer.
| Position written by the tester | Share of all instances |
|---|---|
| No position recorded | 49% |
| Front | 27% |
| Nearside front | 4% |
| Offside front | 3% |
| Central front | 3% |
| Rear | 2% |
From 190,434 recorded instances. Testers can add their own note after the standard wording. The most common on this advisory: “damaged” (2,858), “engine” (804), “exhaust heat shield” (397), “engine undertray” (254), “heat shield” (220), “broken” (167), “and damaged” (129), “wheel arch liner” (68).
What it costs
| Job | Price fitted | Notes |
|---|---|---|
| Replacement clips or screws, DIY | £10–£40 | By registration, from a motor factor or online |
A garage will refix a tray during a service for a few minutes’ labour. A replacement tray is a pattern part on most cars and inexpensive; on some premium models it is a large moulded panel and costs more. Heat shields are priced per shield. Other prices are on the repair costs index.
Can I still drive with this advisory?
Have it refixed before a long motorway trip. A tray that finally lets go at speed can drag, catch the road, or be run over by the car behind. If you hear scraping from under the front, pull over and look.
Enter your reg to see your car’s full MOT history. This advisory two years running usually means the same broken clip was never replaced.
Which cars get this advisory most?
The all-vehicle rate is 0.4 per 1,000 tests. On the models below it is two to five times that.
| Model | Per 1,000 tests | Vs all cars | Tests |
|---|---|---|---|
| Toyota Avensis | 2 | 4.6× | 878,561 |
| Renault Kadjar | 2 | 4.2× | 511,968 |
| Volkswagen Touran | 2 | 4.2× | 848,031 |
| Nissan Qashqai | 2 | 4.1× | 5,273,100 |
| Audi A4 | 1 | 3.3× | 2,768,934 |
| Audi A6 | 1 | 3.2× | 1,247,436 |
| Mitsubishi Outlander | 1 | 3.0× | 658,425 |
| Vauxhall Movano | 1 | 2.8× | 544,309 |
| Honda Civic | 1 | 2.5× | 3,259,563 |
| Peugeot 5008 | 1 | 2.5× | 288,262 |
Model families are grouped by the first word of the DVSA model name, so “Transit” covers every Transit variant. Only models with at least 60,000 tests are ranked.
These are cars with large, low undertrays. The Toyota Avensis, Renault Kadjar, Volkswagen Touran and Nissan Qashqai lead, between four and five times the average, and the Audi A4 and Audi A6 follow. A big tray has more edge to catch and more clips to lose.
The Nissan Qashqai, on more than five million tests, is the one to notice. It is a very common car with a tray that catches speed humps, and every garage has refitted one.
What to do next
- Look underneath. A torch from the front. A corner hanging down, or an empty clip hole, is the whole story.
- Count the missing fixings and buy the right ones. By registration. Cheap generic clips often do not fit the hole size.
- Refix it, or replace it if cracked. Washers under bolts through cracked holes work well. A badly broken tray is cheap to replace on most cars.
- Mention it at the next service. The tray is off anyway for the oil change. Ask them to fit new clips when it goes back on.
Undertray advisory FAQ
What does undertray not fully secure mean on an MOT?
The plastic tray under the engine bay, or a heat shield or piece of sound deadening, has lost some of its fixings or is damaged but is still attached. It is an advisory and the car passes.
Will a loose undertray fail the MOT?
Only if it is likely to fall off. According to DVSA MOT data analysed by PriceMyRepair, 0.6% of 83,373 such advisories failed on an undertray at the next test, among the lowest rates for any advisory.
Can I drive without an engine undertray?
Yes, the car will run and pass an MOT without one. You lose some protection for belts and wiring against spray and stones, a little fuel economy, and on some cars part of the engine cooling airflow. Refitting it is cheaper than that sounds.
How much does it cost to fix?
New clips or screws cost £10–£40 and take minutes. A replacement tray is inexpensive on most cars and priced by model on premium ones. These are estimates and final quotes come from garages.
Why does the undertray keep coming loose?
Speed humps and steep driveways catch the leading edge, and push-fit clips break when the tray is removed for servicing and the old clips are reused. Ask for new clips at every oil change.
Which cars get this advisory most?
Cars with large, low trays: the Toyota Avensis, Renault Kadjar, Volkswagen Touran and Nissan Qashqai, at four to five times the average rate.
How these figures were calculated. According to DVSA MOT data analysed by PriceMyRepair, from the DVSA anonymised MOT test results (Open Government Licence v3.0): 350,943,111 tests. This advisory was recorded 190,434 times; 83,373 of those were followed to the same vehicle’s next test between 180 and 730 days later. “Fails on the same part” means a failure at that next test under the same defect code and naming the same component, on either side of the vehicle. Testers do not always name a component the same way twice, so the figure is a floor. Method and how to cite.