Diagnose and rectify light vehicle chassis system faults

Business Sectors (Suites): Maintenance and Repair - Light Vehicle
Developed by: IMI
Approved on: 30 Mar 2020


This NOS is about diagnosing and rectifying faults occurring within vehicle steering, suspension and braking systems.

Performance criteria

You must be able to:

P1 use suitable personal and vehicle protective equipment when using diagnostic methods and carrying out rectification activities
P2 support the identification of faults, by reviewing vehicle:

P2.1 technical data
P2.2 diagnostic test procedures
P3 prepare the vehicle systems and work area for safe working procedures as appropriate to the vehicle
P4 prepare, check and use all the required equipment following manufacturers' instructions 
P5 use diagnostic methods which are relevant to the symptoms presented
P6 collect diagnostic information in a logical and systematic way relevant to the diagnostic methods used
P7 collect sufficient diagnostic information to enable an accurate diagnosis of chassis system faults
P8 identify and record any system deviation from manufacturer’s tolerances accurately
P9 accurately ensure your assessment of dismantled sub-assemblies, components and units identifies their condition and suitability for repair or replacement
P10 inform the relevant person(s) promptly where repairs are uneconomic or unsatisfactory to perform
P11 carry out all rectification activities following: 

P11.1 manufacturers' instructions
P11.2 your workplace procedures
P11.3 health. safety and environmental requirements
P12 work in a way which minimises the risk of:

P12.1 damage to other vehicle systems
P12.2 damage to other components and units
P12.3 contact with leakages
P12.4 contact with hazardous substances
P13 ensure all repaired and replacement components and units conform to the vehicle operating specification and any legal requirements
P14 correctly adjust components and units when necessary to ensure that they operate to meet system requirements
P15 record and report any additional faults you notice during the course of work promptly
P16 use testing methods which are suitable for assessing the performance of the system rectified
P17 ensure the chassis system rectified performs to the vehicle operating specification and any legal requirements prior to return to the customer
P18 ensure your records are accurate, complete and passed to the relevant person(s) within the agreed timescale in the format required
P19 complete all system diagnostic activities within the agreed timescale
P20 report any anticipated delays in completion to the relevant person(s) promptly 

Knowledge and Understanding

You need to know and understand:

Legislative and organisational requirements and procedures *

K1 the legislation and workplace procedures relevant to 

K1.1 health and safety
K1.2 the environment (including waste disposal)
K1.3 appropriate personal and vehicle protective equipment
K2 legal requirements relating to the vehicle (including road safety requirements)
K3 your workplace procedures for:

K3.1 recording fault location and correction activities
K3.2 reporting the results of tests
K3.3 the referral of problems
K3.4 reporting delays to the completion of work
K4 the importance of working to recognised diagnostic and rectification procedures and processes and obtaining the correct information for diagnostic and rectification activities to proceed
K5 the importance of, documenting diagnostic and rectification information
K6 the importance of working to agreed timescales and keeping others informed of progress
K7 the relationship between time, costs and productivity
K8 the importance of reporting anticipated delays to the relevant person(s) promptly

Electrical and electronic principles *

K9 electrical and electronic principles associated with *chassis systems, including types of sensors and actuators, their application and operation
K10 how electrical and electronic chassis systems operate, including electrical component function, electrical inputs, outputs, voltages and oscilloscope patterns, digital and fibre optics principles
K11 the interaction between electrical, electronic and mechanical components within vehicle chassis systems
K12 how chassis electrical systems interlink and interact, including multiplexing
K13 electrical symbols, units and terms
K14 electrical safety procedures 
K15 the hazards associated with working on or near high energy electrical vehicle components

Use of diagnostic and rectification equipment

K16 how to prepare and check the accuracy of diagnostic testing equipment
K17 how to use diagnostic and rectification equipment for chassis mechanical, electrical, hydraulic/pneumatic and fluid systems, specialist repair tools and general workshop equipment

Chassis faults, their diagnosis and correction *

K18 how *chassis mechanical, electrical, electronic, hydraulic/pneumatic and fluid systems are constructed and operate
K19 how chassis mechanical, electrical, electronic, hydraulic/pneumatic and fluid systems are dismantled, reassembled and adjusted to manufacturers specifications
K20 the types and causes of chassis mechanical, electrical, electronic, hydraulic/pneumatic and fluid system, component and unit faults and failures 
K21 chassis mechanical, electrical, hydraulic/pneumatic and fluid component and unit replacement procedures, the circumstances which will necessitate replacement and other possible courses of action
K22 how to find, interpret and use sources of information on chassis electrical operating specifications, diagnostic test procedures, repair procedures and legal requirements
K23 vehicle operating specifications for limits, fits and tolerances relating to chassis mechanical, electrical, electronic, hydraulic/pneumatic and fluid systems for the vehicle(s) on which you work
K24 how to select the most appropriate diagnostic testing method for the symptoms presented
K25 how to carry out systematic diagnostic testing of chassis mechanical, electrical, electronic, hydraulic/pneumatic and fluid systems using a prescribed process or format
K26 how to assess the condition evident within chassis mechanical, electrical, electronic, hydraulic/pneumatic and fluid components and units
K27 how to interpret test results and vehicle data in order to identify the location and cause of vehicle system faults
K28 how to carry out the rectification activities in order to correct faults in the chassis mechanical, electrical, electronic, hydraulic/pneumatic and fluid systems
K29 the relationship between test methodology and the faults repaired – the use of appropriate testing methods
K30 how to make cost effective recommendations for rectification


1. Chassis systems* are:

1.1. steering
1.2. suspension
1.3. braking

2. Diagnostic methods are:

2.1. measurement
2.2. functional testing
2.3. electrical and electronic systems testing

3. Diagnostic testing is defined as:

3.1. verify the fault
3.2. collect further information
3.3. evaluate the evidence
3.4. carry out further tests in a logical sequence
3.5. rectify the problem
3.6. check all systems

4. Equipment is:

4.1. diagnostic and rectification equipment for chassis mechanical systems
4.2. diagnostic and rectification equipment for chassis electrical systems
4.3. diagnostic and rectification equipment for chassis hydraulic/pneumatic and fluid systems
4.4. specialist repair tools
4.5. general workshop equipment

5. Faults are:

5.1. mechanical
5.2. electrical and electronic
5.3. hydraulic/pneumatic and fluid

Scope Performance

Scope Knowledge





This section contains examples and explanations of some of the terms used but does not form part of the standard.

Agreed timescales:
Examples include: manufacturer's recommended work times, job times set by your company or a job time agreed with a specific customer.

Chassis or Frame area:
Suspension systems, assisted steering systems, non-assisted steering systems, braking systems, ABS/traction control, wheels and tyres.

Chassis system faults:
These are faults that require a multistage inspection and a series of test results to identify the cause.

Diagnostic information:
This relates to mechanical condition, including wear, run out, pressures, flow, leakage and electrical measurements such as voltage and pulse displays, electronic systems data, including fault codes, sensor measurements and control unit outputs and/or signals.

Functional testing:
Examples include: suspension and steering alignment, performance testing and road testing where relevant.

Hydraulic/pneumatic and fluid systems:
Examples are: hydraulic braking systems, hydro-pneumatic suspension systems, power steering.

Examples include: servicing, dismantling for further inspection and test, repair and replacement.

Rectification activities* are defined as:
A suitable repair or replacement that rectifies the fault(s) identified from the diagnostic activities carried out.

These can be any of the following – light vehicles. Additionally, these vehicles may be SI, CI, Hybrid, Electric or Alternative fuel vehicles.

Alternative fuel:
This is defined as any type of fuel that may be used to power an internal combustion engine, examples would include LPG, bio ethanol etc.

Links To Other NOS

External Links

Version Number


Indicative Review Date

31 Mar 2024





Originating Organisation


Original URN


Relevant Occupations

Engineering, Light Vehicle Diagnostic Technician (Automotive), Vehicle Trades

SOC Code



Diagnose; rectify; motor; vehicle; chassis; systems; faults; light; vehicle; brakes; chassis; ABS; traction; control; EBS; EBD; steering; PAS