2002 20litre Hpi 60k

[coastline taxis]

Hi after having to be dragged kicking and screaming into the world of car diagnostic in order to keep up with modern cars im really getting into it now and find the scanner an important tool. However im still learning so what i want to know is can a sensor malfunction and not show up as a trouble code or does that just not happen. The reason im asking is that the car mentioned above shows no codes or faults at all yet when taking out on the road it keeps giving all the symptons of an air mass fault loss of of power and fluffy tick over. vacum pipes/air intake pipes/turbo/timming/egr valve all checked and fine. So swapped over to live data and taking out onto road all injectors have equal pressure and all other data is normal as we compared it to a one that i own after doing live data on that one and comparing it. The loss of power isnt dramatic it just wont go over 70 and the tickover goes fro 700 rpm down to 600 rpm but dosent cut out.

[paul.h]

Maybe the problem is not bad enough to give a fault code. I think on Saabs the crank position sensor does not give a fault code and as it got worse poor running would occur and eventually the car may not run at times/all the time - may not apply here. Poor tick over may be caused by carbon build up in the throttle body / throttle plate area.

[techbod]

in most cases a code is just a guide and the sensor is doing its job ( does your code reader store soft codes? ) these are not important codes and only put the engine warning light on when it happens 3 times, a fault code reader is a tool you need since OBD 1/II/EOBD/CAN came in so not like the old days when you could track a fault by simple tests today you need much more like an oscilloscope/multi meter/ data and that's all supplied through a laptop and with good software and only thing that isn't supplied is knowledge of how things work,

 

main thing to remember is when a fault code comes up you have to think what else could cause it and not just the sensor and I call it the domino effect

[coastline taxis]

in most cases a code is just a guide and the sensor is doing its job ( does your code reader store soft codes? ) these are not important codes and only put the engine warning light on when it happens 3 times, a fault code reader is a tool you need since OBD 1/II/EOBD/CAN came in so not like the old days when you could track a fault by simple tests today you need much more like an oscilloscope/multi meter/ data and that's all supplied through a laptop and with good software and only thing that isn't supplied is knowledge of how things work,

 

main thing to remember is when a fault code comes up you have to think what else could cause it and not just the sensor and I call it the domino effect

ok so the sensors just report that there is a fault in the area that they monitor and if that fault isnt strong enough then it wont show a fault code. so try cleaning throttle and crank

Thanks

[techbod]

a crank sensor will always give a failed reading if the engine isn't running that's called a static diagnostic test via a diagnostic tool and that's normal because it only gives a signal when the engine is running so any fault with that would be intermittent unless it was loose and in both cases it would produce poor engine responce,

if it were shot then the car wouldn't even start no spark/fuel pressure because it switches them on when ignition is switched on which is called a dynamic test via diagnostic tool and that's that one covered now the throttle body on the C5 is motorised and not cable driven and if it were gunked up with carbon and oil deposits the butterfly valve would hesitate or stick and cause engine to idle poorly and impair throttle responce,

 

it gets interesting when you know how they work ;)