Page 2 - Help With Specific Faults
Engine will not run / fuel shut off - using a diagnostic computer clear the fault codes in the engine management system, this should release the fuel pump, if not also clear fault codes in body control module & airbag ecu, if not do a global clear and clear fault codes in every ecu available, if not try cycling central locking after clearing all codes. If still no start then you may have a secondary fault that needs investigation, time to consult your mechanic.
Electronic power steering not working - check for diagnostic fault codes, if it's related to crash then using a diagnostic computer re-calibrate the electronic power steering system. Different manufacturers have different procedures. If your diagnostic computer cannot do it then consult a specialist mechanic for your brand of vehicle. If the fault is a secondary fault such as damaged wiring or sensor then repair that fault & erase fault codes.
A.B.S / traction light on - using a diagnostic computer re-calibrate the a.b.s / traction system. Different manufacturers have different procedures. If your diagnostic computer cannot do it then consult a specialist mechanic for your brand of vehicle. If the fault is a secondary fault such as damaged wiring or sensor then repair that fault & erase fault codes.
Diagnostic Fault Codes - Problems & Solutions....
Defective airbag module / internal error - try erasing the fault code a few times with a diagnostic computer, turning ignition off & on between attempts. If it doesn't work the airbag module will be faulty and needs replacing, this can often happen after an airbag deployment due to the current flowing through them when triggering airbags or seat belts.
No comms with another module / ecu - check the other module in question, the fault may be on another system & not the airbag system.
High resistance on a circuit - you have a bad connection or open circuit on that circuit in question - (don't forget the circuit comprises of components & wiring) usually a connector not connected properly, a damaged connector, a broken wire, moisture/corrosion in a connector. If the securing tab on the back of the connector is in any way damaged this can cause this problem. Just because the plug is in it does not mean it's right, the securing tab locks the connector in and creates a tight friction connection. Damaged plugs cause a lot of problems - don't overlook them, don't glue them in, they need to be perfect. Normal ohms range is about 2-3 ohms.
Low resistance on a circuit - this can be a short on the circuit but also can be loose connectors. Check the connectors at the component in question and the airbag module checking for bent pins, damaged connectors or loose connectors. They need to perfect and free from damage. Faulty connectors with missing securing tabs often cause most problems. Don't glue them - renew them ! If all the connectors , securing tabs and internal pins are fine then start checking the circuit for any shorts, using a multi-meter or visual checks. Remember factory fitted is usually fine, the faults are mainly where the repairer has been working, think what have human hands been doing on this vehicle. Normal ohms range is 2-3 ohms.
Short on a circuit - the circuit in question is shorting, often it's shorting to earth which is a sign that you have a wire with damaged insulation which is making contact with the vehicle body somewhere. This could be a seat airbag wire touching the seat frame or a dash airbag that has been screwed through or trapped. Think about the circuit in question and what has been tampered with, where have human hands been. Is the connector damaged, have pins been bent and are touching, has a plastic lug broken off inside the module or component plug causing a busbar to engage and create a short. Often airbag components have busbars installed so they purposefully short when the plug is disconnected so again if connectors and plugs are in any way damaged or plastic lugs are broken then these simple things cause problems which people seem to dismiss or overlook. Check those plugs and wires !
Trigger line coefficient / coherency - usually incorrect module for vehicle. Either the module is programmed for something the vehicle is not fitted with or the vehicle is fitted with something the module does not think it should have. For diagnosis you can try disconnecting the component in question or change the module. Do not leave airbag equipment inactive if it should be installed on that vehicle.
Triggering line fault / triggering / firing loop fault - this simply means you have a fault on that circuit in question. For example 'Drivers airbag triggering line stage 1 ; high resistance' - this means you have a high resistance on the drivers airbag stage 1 circuit. Triggering line or loop is not crash data, this is only referring to a circuit. Think of triggering line or triggering loop or firing loop as the wires that run from the module to that component.
Stage 1 & stage 2 faults - some airbags have two plugs and these are named stage 1 or 2 or A or B and are usually marked where they terminate on the airbag. Stage 1 & 2 or A & B refers to one of the two plugs, they are identified in wiring diagrams to aid diagnosis.
Drivers module fault / passenger module fault - some vehicle manufacturers like Nissan like to call their airbags - 'modules' so don't always assume that 'module' means the airbag ecu. Read the fault code carefully because 'drivers module' means drivers airbag in the steering wheel, so don't be caught out on that one.
Check sum error - airbag module is defective and needs replacing.
Impact detected - crash data needs clearing - module needs resetting
Crash event storage full & locked - crash data needs clearing - module needs resetting
Some Useful Terminology....
Inner pretensioner - seat belt tensioners located on side of seats near handbrake
Outer / anchor pretensioner - seat belt tensioners located on the inner sills (some vehicles of x2 tensioners on each front seat)
Retracting / retractor pretensioner - seat belt reel located on post
Lap belt - seatbelt tensioner located on seat side near door (not handbrake side)
Rear row / 2nd row pretensioners - rear seat belt tensioners
3rd row - rear - rear seats - i.e final row in 7 seater
Drivers airbag - steering wheel airbag
Passengers airbag - passenger front airbag in dashboard
Submarine airbag - airbag located under front of seat
Knee airbag - airbag located in lower dash under steering wheel
Head / curtain / roof airbag - airbag located in roof lining
Side airbag - airbag located in seats or doors
Pop up roll bars - convertible pop up bars in back seat / parcel shelf area
Pedestrian system - bonnet lifting system
Squib - just a connector or plug on an airbag or sometimes the spiral connector behind drivers airbag in steering wheel but a squib can be on any airbag not just drivers.
Clockspring - spiral connector behind steering wheel , sometimes incorporates stalks
Crash sensor / impact sensor - sensors located around the vehicle to detect crash
R.C.M / Airbag Module / Airbag ECU / SRS Module - airbag control module, usually under centre console area
O.C.S / Occupancy classification system - system for detecting passenger seat occupants
PAD - Passenger airbag deactivation system / switch
Summary with words of advice
If the airbag light is on after the module has been reset it is usually because of a fault on the vehicle & is rarely anything to do with the module or the reset - (when done by us).
Unfortunately customers find this hard to believe and nearly always assume the module is at fault rather than going through the process of diagnosing and repairing the fault so firstly we like to say - have faith in our work and trust the module reset, look at the car for faults.
Most of the time the fault keeping the airbag light on is really simple - don't look too deeply into it & apply common sense.
Take notice of the fault codes and consider which items on that circuit have been touched by the repairer or the opposite could apply, perhaps the fault code is indicating a fault on a circuit which hasn't been touched - could there be a blown component you have missed like a seat belt pretensioner. Either way that circuit needs further investigation.
When using fault codes & looking for faults on circuits you want to apply the logic;
What has blown - have we covered everything
Could the crash have damaged wiring
Where have human hands been working whilst fixing this salvage vehicle - most common faults are module not bolted down, pretensioners not replaced & problems with connectors - simple as that !
TOP FAULTS FOR SALVAGE CARS;
Seat belt pretensioner not replaced or been sold a deployed one
Damaged connectors, damaged locking tabs - they need to be 100% perfect - no getting away from this
Connectors not secured by the locking tab - they may feel fully home but they need the locking tab to make a proper connection
Connectors not in properly - sometimes the locking tab pushes in before the connector was fully home, always insert connector by holding the sides and then finally push in the locking tab.
Airbag module not bolted down or an earth wire not connected
Airbag module not connected up properly and the plugs have not gone fully home & locked in
Airbag module pins bent when refitting plugs
Airbag module plastic lugs broken in the plug receptacle
Wrong crash sensors used during repair - incorrect part numbers
Blown airbag fuse
Trapped wires when refitting airbags, dashes, seat bases etc
Diagnostic computer saying fault is on left hand when it is really the right hand, we have had computer mix up sides on uk cars so always worth unplugging a component on the opposite side to see if it's giving correct information.
Previous repairs - resistors put in place of airbags, module swapped for wrong one
Faulty airbag module - cannot be ruled out as they can be faulty following an airbag deployment