R34 25GT Engine Light 21

[CF.Panda]

Hello, first of, I’ve looked at many threads on this code but none have helped me, if you know one that will help me feel free to post a link.

 

Now to my problem. Recently I was driving and noticed the check engine light came on. I went home and did the test to see what code it gave. I got the 21 code but everything seems fine with the car, no misfire, idle is good, acceleration is the same as when I bought it. I mean no signs of obvious failure. If no misfire is happening I can rule out the coil packs right? Which is about 98% of posts saying it is. If anyone has had this happen and found the issues let me know please. No other lights are on.

 

The car WAS due for an oil change. I since then changed it so idk if that triggers code 21. Either way it hasn’t turned off.

[GTSBoy]

Have you done 10x restarts since it came on?

[joshuaho96]

4 hours ago, CF.Panda said:

Hello, first of, I’ve looked at many threads on this code but none have helped me, if you know one that will help me feel free to post a link.

 

Now to my problem. Recently I was driving and noticed the check engine light came on. I went home and did the test to see what code it gave. I got the 21 code but everything seems fine with the car, no misfire, idle is good, acceleration is the same as when I bought it. I mean no signs of obvious failure. If no misfire is happening I can rule out the coil packs right? Which is about 98% of posts saying it is. If anyone has had this happen and found the issues let me know please. No other lights are on.

 

The car WAS due for an oil change. I since then changed it so idk if that triggers code 21. Either way it hasn’t turned off.

Oil change does not trigger code 21. Code 21 is for coilpacks primary side connection. You can try to clear the code with a battery disconnect, hold down the brake pedal to drain capacitors through the brake lights with the ignition on for 10-15 seconds before you reconnect the battery. I have seen R35 coil conversion permanently cause this code with no ill effects so it might be the resistance it wants to see isn't quite right on one or more coilpacks. Could be inside the ECU, could be the harness, could be a coil. You can test it all if you want or just ignore until the car actually starts misfiring.

[CF.Panda]

21 hours ago, GTSBoy said:

Have you done 10x restarts since it came on?

Yes I have. Probably on my 15x restart.

[CF.Panda]

17 hours ago, joshuaho96 said:

Oil change does not trigger code 21. Code 21 is for coilpacks primary side connection. You can try to clear the code with a battery disconnect, hold down the brake pedal to drain capacitors through the brake lights with the ignition on for 10-15 seconds before you reconnect the battery. I have seen R35 coil conversion permanently cause this code with no ill effects so it might be the resistance it wants to see isn't quite right on one or more coilpacks. Could be inside the ECU, could be the harness, could be a coil. You can test it all if you want or just ignore until the car actually starts misfiring.

So 10/10 times that code is coil packs? I mean if that's the case ill drop the $400USD or so to replace them. I didn't know these cars threw codes before the issue became an issue.

[GTSBoy]

5 hours ago, CF.Panda said:

Yes I have. Probably on my 15x restart.

If it (the code) wasn't still current, it should have gone away by itself by now.

5 hours ago, CF.Panda said:

So 10/10 times that code is coil packs?

No, nothing it 10/10. But it is quite likely. Everything else to do with the ignition could still be responsible (which is wires and connectors). The car is an old piece of shit now, so all the wires and connectors are also old pieces of shit.

[joshuaho96]

6 hours ago, CF.Panda said:

So 10/10 times that code is coil packs? I mean if that's the case ill drop the $400USD or so to replace them. I didn't know these cars threw codes before the issue became an issue.

It's not that straightforward. For example I have had this code because my ignitor/power transistor wires were unplugged. It knows something is wrong but has no idea what it means. If you want to actually diagnose this I recommend following the service manual flowchart for code 21. Ohm out the harness, coilpacks, inspect the ECU, etc. And again, it's entirely possible for there to be no problem at all but if you're running a different coilpack it'll trigger the code because it doesn't like what it sees.