P1999
Thread Starter
Junior Member
Joined: Apr 2019
Posts: 45
Likes: 1
'03 CL55
P1999
2003 CL55. Getting a P1999 code along with P0040 and P0300. The 1999 is the one that I have never seen before. "Load limit is active". Symptoms are car stumbles and misfires when throttle position get over about 25-30% (right about when the s/c kicks in) especially if the throttle is opened quickly
Normal cruising is fine. Idle is fine. Shifts fine. It has new plugs, coils, plug wires, IA sensor, O2 sensors all done at the same time last summer and the car has about 1000km on the new parts it and has run great until this new code hell. Looked up this code, not much specific info.
Car has a Eurocharge tune, headers, belt wrap kit, smaller pulley, split cooling, all the usual tricks. Spoke to Eurocharge, they have never seen this code.
Once the car is shut off and restarted it runs fine until you dip into the throttle again. I have cleared the codes but that isn't the cure.
Thoughts on where to start?
Normal cruising is fine. Idle is fine. Shifts fine. It has new plugs, coils, plug wires, IA sensor, O2 sensors all done at the same time last summer and the car has about 1000km on the new parts it and has run great until this new code hell. Looked up this code, not much specific info.
Car has a Eurocharge tune, headers, belt wrap kit, smaller pulley, split cooling, all the usual tricks. Spoke to Eurocharge, they have never seen this code.
Once the car is shut off and restarted it runs fine until you dip into the throttle again. I have cleared the codes but that isn't the cure.
Thoughts on where to start?
Newbie
Joined: Jan 2026
Posts: 4
Likes: 0
On a 2003 CL55 (M113K), “load limit active” usually means the ECU is going into a protection/limp strategy because it’s seeing another fault. In your case, P0040 and P0300 are the key ones.P0040 is commonly caused by the upstream O2 sensors being swapped (bank 1 and bank 2 connectors crossed) or a wiring issue. That can make the ECU go crazy under load and trigger torque limiting right when boost comes in. P0300 under boost can also be caused by a boost leak or a fuel pressure issue.
Try to confirm the upstream O2 connectors are on the correct banks, then check for boost leaks and verify fuel pressure under load. If you can, log live data during the stumble (fuel trims, MAF, O2/lambda, misfire counts) to narrow it down fast.
Try to confirm the upstream O2 connectors are on the correct banks, then check for boost leaks and verify fuel pressure under load. If you can, log live data during the stumble (fuel trims, MAF, O2/lambda, misfire counts) to narrow it down fast.
