Fault Code 21 - Where to Start

paz

Active Member
Hi All,

Recently did a test and was getting fault codes 21 and 34. Changed the det sensor replaced yesterday and after resetting the fault check it appears this has fixed the fault code 34 problem.

Code 21 is still with me however :roll:

Having done a search, I know this means a fault in the ignition signal circuit, and that I should check the 'harness and connector' and power transistor unit.

BUT I can't find anything recent that seems a simple step-by-step approach to resolving this problem. Can any of you helpful people out there help me out? :)
 

wrc

Member
Had this problem last week.

Heat soak on the power transistor...



Remedy:-

The power transistor sits just below the coil & dizzy, its bolted to a bracket that is bolted to the side of the block. Its soaks up heat from the block and breaks down when it gets hot.

Unbolt the 2 bolts and remove it from its bracket and unplug the connecter. Take 3/4 2 pence pennies , stack them on top of each other and then with electrical tape, tape then to the back of the connector (the metal exposed side). The copper essentially acts as a heat sink and will draw heat out of the sensor.

When you re fit the power transistor, dont fit it back to its original place - re-locate it. I cable tied mine to my boost pipe - anywhere is fine, but essentially just put it somewhere where it can breathe a little better. They suffer this alot in oz where its hotter, but its getting more common over here now as things get older etc.

Job jobbed. Never had a problem since here.

Estimated job time is about 10 whole minutes :lol:
 

paz

Active Member
Thats awesome, will give it a go thanks :-D

Anything else people have had to do to fix code 21?
 

wrc

Member
Essentially its just sensing an ignition breakdown and throwing up a fault code for it. So try the power transistor mod, if that doesnt work its just an ignition related fault so check the usuals i.e. condition of the cap and rotor, condition of the coil, leads arcing out, plugs etc.
 

PobodY

Moderators
Staff member
Mine has got the heatsink from a Pentium strapped to it. - To be honest you'd be pretty hard pressed to overheat the power transistor in the UK; they might have a problem with that in Australia, but the ambient temperature is much higher.

If you do have a problem with it, simply moving off the engine block is the solution; it's supposed to be on the support bracket for the TMIC. - The only reason I moved mine was that I took the bracket out and didn't want to bolt the transistor back onto the block.

I'd be checking the wiring to make sure you haven't lost an earth or snapped one of the little wires. - It could be as simple as the distrubutor rotor or cap need replacing like the man says.
 

GTI-R Nath

New Member
im getting fault code 21 too when im driving for long periods, might try some thermal paste on the power transistor thanks for the tip
 

paz

Active Member
Ok, done the power transistor mod- it didn't work :(

Even after a 2 minute drive fault code 21 comes back. Changed the plugs at the same time, and despite some soot on the plugs, that doesn't seem to have helped.

Next stop is the rotor arm and dizzy cap unless anyone has any other ideas?

One last thought, I have an ignition amplifier- could that be causing any problems?

Cheers

Paz
 

wrc

Member
The part that you just did the heatsink mod to IS your ignition amplifier...! I take it you mean an unrated one?

Next try looking at the cool? Easy to fit a replacement and quite cheap.
 

stumo

Active Member
11 Crank Angle Sensor circuit
12 AFM circuit
13 Engine temp sensor circuit
21 Ignition signal circuit
34 Detonation sensor circuit
43 Throttle sensor circuit
55 No malfunction in the above circuits"


21 is the IGNITION SIGNAL CIRCUIT which includes the wiring and IGN amp module.

It doesn't include plugs, plugleads, dizzy cap or rotor arm, just the wiring to and from the coil, the coil and the wiring to and from the Ign amp.

The ECU isn't clever enough to sense the plugs haven't fired etc

Best get out the multimeter.... i'll have a look at my manuals but they're at work. let you know on monday.
 

Fast Guy

Moderators
Staff member
That's what he said. Power transistor unit is the ignition amplifier. harness & connector is the wiring.
 

bensmith907

New Member
Yea he also said he would check his manual, well thats the hyperlink for it and I quoted what the manual says incase the link doesn't work.

im not stealing thunder- just backing up his diagnosis with the manual.

I can do the wiring diagrams too if you like-
 
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Fast Guy

Moderators
Staff member
Ahh, I might have misunderstood what you wrote, it came across to me as you were trying correcting him.
I put a copy of the manual page in the sticky to make it easier for everyone to find.
 

stumo

Active Member
have a look on page 943 of the online manual and follow the chart etc. ECU connector is on page 1090

Coil resistances is on page 1092

Ign amplifier resistances is on page 1093

make sure you understand the connection diagrams (ie which way round to look at them etc)


If you can swap the ign amp for a known good one and see if the problem goes away is the easiest thing to do.
 
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bensmith907

New Member
Ahh, I might have misunderstood what you wrote, it came across to me as you were trying correcting him.
I put a copy of the manual page in the sticky to make it easier for everyone to find.
Ha Ha, there's no chance I would correct stumo (lower case s). not after him ripping into Pulsarmad20 last week. true comedy!
 

paz

Active Member
Hi All,

Just seen this, not had chance to persue much thanks to work.

I think I'll pick up an ignition amplifier if possible and go from there.

Not sure my usual garage are good enough for stuff like this - any recommendations on people who know pulsars in the NW?

Cheers

Paz
 

bensmith907

New Member
Hmmm. just hit a massive pot hole and the engine started dying and now its cold wont start... anyone had anything in the ignition circuit fail from a bump?

fault code 21, engine doesnt even splutter

I've checked the coil and it only just above 1ohm for step 1 so that seems fine, the ignitition amplifier fails the test so im getting a new one of those, can anyone think of anything else it might be if the amplifier doesnt cure it?

thanks
 
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