Checked 27 October 2026. Format facts are from the OPC's DFFT test page and its candidate guide, and the standard's scope from RSSB's 3751-FAQ on RIS-3751-TOM issue 4, all read on 27 October 2026. Companies choose their own extra tests, so check your invitation.
The Driver Fault Finding Test (DFFT) is a timed test from The OPC in which you read 20 diagrams of a train system, each with a display panel and a fault finder guide, decide which fault to solve first and give the code to solve it. It is timed, but the OPC does not publish how long candidates get. It is not one of the core tests every train company uses, so you sit it only if the company you applied to chooses it, and no pass mark is published.
Checked on 27 October 2026 against the OPC's DFFT test page, its DFFT practice page and its candidate guide, and RSSB's FAQ on the train driver selection standard. Our own method and the worked example are labelled as ours. ProSyllabus is an independent study site. It is not part of RSSB, the Office of Rail and Road, The OPC or any train company, and nothing here is official test material.
What the DFFT measures
The OPC, which publishes the test, says the test gives the assessor an insight into your potential to use logical thinking to identify and solve faults "in an efficient, safe and effective manner". It also says the test assesses the ability to think logically, check details, make effective decisions, follow instructions and work under time pressure, in order to find and solve faults on a train.
That is a different skill from attention, the criterion under which RSSB lists the Group Bourdon and TEA-Occ: the DFFT asks you to apply a set of rules to a situation and reach a decision. The OPC says the diagrams show "a new and innovative train system", and that each comes with the display panel, technical information about the train and the fault finder guide, so the test is built around the information it gives you.
The format, as the OPC publishes it
| Detail | What the OPC says |
|---|---|
| Questions | 20 questions: 20 diagrams of a train system |
| Time | Timed. The page lists "Assessor Time" as approx. 45 minutes; it does not say how long candidates get, so take your timing from your invitation and the instructions on the day. |
| With each diagram | A display panel showing the train's instruments and dials, some technical information about the train, and a fault finder guide |
| The fault finder guide | What to do once you have identified a fault, and the order of priority for solving faults |
| Your answer | Decide which faults to solve, then identify a code for solving the fault and any other action needed |
| Materials | Administration and candidate instructions, a question booklet, the fault finder guide, a fault report form, a scoring booklet and a practice leaflet |
| Training | Test User Occupational Ability (TUO-A), formerly known as Level A |
| Job roles | Train driver and tram driver |
The DFFT page does not say whether the test is on paper or online. The OPC's practice page refers to sitting "an online or paper version of the test", so check your invitation. The DFFT page does not say how answers are scored, and it does not publish a pass mark.
Where the DFFT sits in train driver selection
RSSB's standard RIS-3751-TOM issue four sets out the psychometric tests every train company uses. The OPC's candidate guide calls these the "core tests": the Group Bourdon, the Trainability for Rules and Procedures tests (parts 1b and 2), TEA-Occ, the Vienna Test System and the Multi Modal Interview. The DFFT is not on that list.
Both official documents leave room for it. The OPC's guide says "some companies also make use of extra tests and exercises" that they ask candidates to pass, and RSSB's FAQ says companies "may also use other assessments to support decision-making in train driver selection". No source we read says which companies use the DFFT. So whether you sit it, and at which stage, depends on the company you applied to choosing it as an extra. Your invitation and the practice materials the company sends will tell you. The full list of standard tests is in our train driver psychometric tests guide, and the order of the day is in our assessment day guide.
How to work a DFFT-style question: our method
The OPC does not publish a method, so this is ours, built from what its page says the test asks: identify the faults, use the order of priority, then find the code and any other action.
Eight steps for every diagram (our method)
- Learn the priority order first. Before the clock matters, read the fault finder guide's order of priority until you know it without looking.
- Scan the display panel. Compare every reading with its normal range and note each one that is out of range.
- Group the bad readings by system. Several bad readings in one line of the diagram are often one fault showing up in several places.
- Take the highest-priority system only. A lower-priority fault can be real and still be the wrong answer.
- Start at the symptom and work back. Begin with the bad reading furthest along the line, then move back towards the supply.
- Clear the shared supplies. If something else on the same breaker or supply works normally, that supply is fine.
- Stop at the first item that is wrong. The fault is the first item, working back, that is not doing what it should.
- Match the code, then check its conditions and the extra actions. Many codes look alike; the conditions tell them apart.
Our advice, not the OPC's. Use the instructions and practice materials you are sent; they take priority over anything here.
A worked example, start to finish
This example uses our own invented system and our own guide. It shows the method, not the real test's content.
Battery→Breaker CB1→Compressor→Main reservoir→Brake pipe
Breaker CB1→Door controller→Doors closed lamp
Battery→Heating unit→Saloon temperature
Our own invented system for teaching the method, not a diagram from the DFFT. In the worked answer below, the item that turns out to be at fault is outlined in red.
| Display panel reading | Shows | Normal |
|---|---|---|
| Battery voltage | 110 V | 100 to 120 V |
| Breaker CB1 | Closed | Closed |
| Compressor running lamp | Off | On whenever the main reservoir is below 8 bar |
| Main reservoir | 5.0 bar | 7 to 9 bar |
| Brake pipe | 3.5 bar | 4.5 to 5.5 bar |
| Doors closed lamp | On | On |
| Saloon temperature | 29 °C | 18 to 25 °C |
Our example fault finder guide
- Order of priority: 1 brakes and air supply; 2 electrical supply; 3 doors; 4 saloon comfort. Solve only the highest-priority fault.
- A1 Compressor not running while the main reservoir is low: reset the compressor at the cab switch.
- A2 Compressor running but the main reservoir is low: isolate the unit and call control.
- A3 Brake pipe low while the main reservoir is normal: apply the emergency brake and call control.
- P1 Breaker CB1 open: reset CB1 once.
- P2 Battery below 100 V: call control.
- C1 Saloon temperature out of range: reset the heating at the panel.
- Extra action S: for any priority 1 fault, also tell the signaller before moving.
Invented by ProSyllabus for this example. The real DFFT has its own guide and codes, which you see on the day.
The answer, step by step
- Bad readings: compressor lamp off, main reservoir 5.0 bar, brake pipe 3.5 bar, saloon temperature 29 °C. Everything else is normal.
- Group them: the first three sit on one line (compressor, main reservoir, brake pipe), so they are probably one fault. The temperature is a separate system.
- Priority: the air line is priority 1, the temperature priority 4. Ignore the temperature, even though it is a real fault.
- Work back: the brake pipe is low because the main reservoir feeding it is low. The main reservoir is low, so the compressor should be running, but its lamp is off.
- Clear the supply: the battery reads 110 V and CB1 is closed. The doors closed lamp, on the same breaker, works. So power reaches the compressor.
- First item that is wrong: the compressor. It has power and should be running, and is not.
- Code: A1 fits (compressor not running, main reservoir low). A2 needs the compressor running; A3 needs the main reservoir normal. Neither fits.
- Final answer: A1, plus extra action S, because it is a priority 1 fault.
The two traps: answering C1 because the temperature fault is easy to see, and answering A3 because the brake pipe reading looks the most serious.
Practise the core test every company uses
Fault finding is an extra; the Group Bourdon is not
We do not sell DFFT practice. Our concentration trainer is for the attention part of the core tests: timed sheets of dot groups, with missed and wrong marks counted apart. Level 1 is free with no sign-in.
Play level 1 freeIndependent practice by ProSyllabus. Not the official test, not a copy of it, and not produced or checked by RSSB, an assessment centre or a train company.
Mechanical comprehension: is it still used?
The standard's test list has no mechanical comprehension test, and neither does the OPC's list of core tests. Because companies may add extra tests, a company could still use one, so read your invitation rather than any general list, ours included.
If you are asked to sit one, mechanical comprehension tests commonly use four kinds of question. These descriptions are ours, not from an official source:
| Type | What it asks | The idea to know |
|---|---|---|
| Gears | Which way, and how fast, a gear turns when another drives it | Meshed gears turn opposite ways; speed changes with the ratio of teeth |
| Levers | The force needed to lift a load, or where to put the pivot | Force times distance from the pivot is equal on both sides |
| Pulleys | How much force lifts a load with a given arrangement | More rope sections holding the load means less force, over a longer pull |
| Forces | Which way an object moves, falls or tips under given forces | Balance, friction, and the centre of gravity |
Two sample items (ours)
- 1. Gears. Gear A has 12 teeth and drives gear B, which has 36 teeth, directly. A turns clockwise at 90 turns a minute. How does B turn? (a) clockwise, 270 a minute; (b) anticlockwise, 30 a minute; (c) clockwise, 30 a minute; (d) anticlockwise, 270 a minute. Answer: (b). Meshed gears turn opposite ways, and B has three times the teeth.
- 2. Levers. A 1.6 m bar rests on a pivot 0.4 m from the end that sits under a 600 N load. Ignoring the bar's weight, what force pressed down at the other end will lift the load? (a) 150 N; (b) 200 N; (c) 600 N; (d) 1,800 N. Answer: (b). 600 x 0.4 = F x 1.2, so F = 200 N.
Our own items. Not official test material, and not a copy of any test.
Common mistakes
What costs marks in a test like this (our view)
- Solving the fault you saw first instead of the highest-priority one.
- Stopping at the symptom. The bad reading is often downstream of the fault, not the fault itself.
- Picking a code from its name alone without checking its conditions.
- Forgetting the extra action the guide adds to some faults.
- Spending too long on one diagram. The OPC says the test is timed and assesses the ability to work under time pressure.
- Skipping the practice leaflet. The OPC lists a practice leaflet among the test materials; read it before the day.
A 7-day plan before a fault finding test
| Day | What to do (our plan) |
|---|---|
| 1 | Read the practice materials your company sent, all of them, and note the instructions you are unsure of. |
| 2 | Work the example above with the answer covered. Write each step down. |
| 3 | Draw two simple systems of your own (a supply, a breaker, two lines) and break one item. Trace back to it. |
| 4 | Redo the practice materials against a clock, at the timing your instructions give, and mark yourself honestly. |
| 5 | Go back over every miss: was it priority, tracing, the code's conditions or the extra action? |
| 6 | A short timed session on the core attention tests, which you will sit at every company. |
| 7 | Rest. Check the time, place, ID and glasses your invitation asks for. |
Pass marks, results and what happens if you fail
No pass mark for the DFFT is published. The OPC's candidate guide says the scores needed to pass are not given to candidates. Where The OPC carried out your assessment and you were unsuccessful, you can ask it for feedback within 3 months of your assessment date; feedback is verbal, gives no scores, and there is none for successful candidates.
For the standard tests, RSSB's FAQ says the standard does not set pass marks; RSSB recommends them and each train company decides which to use. It also says any test outside the standard process is outside the standard's scope. RSSB's attempt limits and waiting periods are written for the standard process, so what a failed DFFT means for applying again is not something RSSB's FAQ answers. Ask the company or assessment centre. For the standard tests, see our guide to retakes and pass rates.
Frequently asked questions
What is the pass mark for the train driver fault finding test?
It is not published. The OPC says the scores needed to pass are not given to candidates, and it does not give scores in feedback. No source we read says what standard applies to the DFFT, so ask the company you applied to.
How long is the DFFT?
The OPC says it has 20 questions and is timed. Its page lists an assessor time of about 45 minutes but does not say how long candidates get, so check your invitation and the instructions on the day.
Do all train companies use the DFFT?
It is not one of the core tests set by RSSB's standard. The OPC says some companies use extra tests and exercises, but no source we read says which companies use the DFFT, so check your invitation.
Can I retake the DFFT if I fail?
RSSB's FAQ says tests outside the standard process are outside the standard's scope, so its attempt rules do not answer this. Ask the company or the assessment centre. If The OPC assessed you and you were unsuccessful, you can ask it for feedback within 3 months.
Is the DFFT the same as a mechanical comprehension test?
No. The DFFT tests logical fault finding using a guide and a display panel. Mechanical comprehension tests ask about gears, levers, pulleys and forces, and are not in the standard's list of tests.
Where can I get DFFT practice?
The OPC says companies may send DFFT practice material, and it sells a 15-question DFFT Practice PDF (8.99 pounds on 27 October 2026). It recommends authorised practice material from OPC Assessment for its tests.
The concentration trainer
Practise the attention tests every company uses
- Level 1 free with no sign-in; levels 2 to 10 unlock with one payment, no subscription.
- From 48 to 126 groups a sheet, three to six sheets a run, 40 to 50 seconds a sheet.
- Freshly generated sheets for every run, so you are not repeating a sheet you have learned.
- Accuracy, groups per minute, and missed and wrong marks counted apart, by sheet and by row.
The price is on the trainer page.
Start with level 1 freeIndependent practice by ProSyllabus. Not the official test, not a copy of it, and not produced or checked by RSSB, an assessment centre or a train company.
New to the process? Start with how to become a train driver in the UK and our Group Bourdon practice guide. All our guides on this assessment are on the UK train driver exam page.
More in this series
- Group Bourdon test practice: free sheets and a 14-day plan
- The TEA-Occ test: what it is and how to prepare
- Every UK train driver psychometric test explained
- Free practice tests compared
- How to pass the Group Bourdon
- Pass rate and retake rules
- The assessment day, step by step
- Group Bourdon pass mark and scoring
- ADHD, dyslexia and the medical
- How to become a train driver in the UK
- Train driver interview questions: the MMI, the DMI and STAR
- Northern trainee train driver
- How to become a Tube driver
- GWR trainee train driver
- Avanti West Coast trainee train driver
- ScotRail trainee train driver
- LNER trainee train driver
- Southeastern trainee train driver
Sources
- official — The OPC (OPC Assessment): "Driver Fault Finding Test (DFFT)" test page (read 27 Oct 2026): what it measures, 20 questions, timed, approx. 45 minutes assessor time, the fault finder guide, the materials
- official — The OPC: "Driver Fault Finding Test (DFFT) Practice" (read 27 Oct 2026): 15 questions, PDF, £8.99; similar to but not the same as the real test
- official — The OPC (a registered assessment centre): "Train Driver Assessment: A guide for candidate's who undertake their assessment with The OPC" (read 27 Oct 2026): the tests, hints and tips, the day, results and feedback
- official — RSSB and the Rail Assessment Centre Forum: 3751-FAQ, "Frequently asked questions", issue one, on RIS-3751-TOM issue four "Psychometric Assessment in Train Driver Selection" (read 27 Oct 2026): the tests by selection criterion, attempts, pass marks, validity, practice materials, minimum age
official = a document published by the conducting body. reported = a news or coaching site we could not check against an original. Where sources disagree this page says so rather than picking one.
