BMW ignition coils do go faulty from time to time. The ignition coils shown in figure 1 were from a 1999 BMW 323i. The vehicle came to us with a check engine MIL on. The technician noticed that there were ignition misfires present. Running module scan with our BMW GT1 diagnostic system confirmed the technician's thoughts. The GT1 revealed that the number 4 cylinder was misfiring.
The technician removed the number 4 ignition coil to inspect for any irregularities. The spark plug was properly torqued, but the ignition coil itself had signs of arcing, and the plastic housing was melted as well. See the red circles in figure 1. With this discovery, the technician decided to remove all of the ignition coils for inspection. Sure enough, all of the ignition coils were suffering from the same affliction.
This vehicle also had fault codes for oxygen sensors. The technician recommended to the customer that the four oxygen sensors, six ignition coils, six spark plugs, and the fuel filter be replaced. Also recommended was updating of the DME with the latest software version. The customer authorized the repairs. After the repairs were completed, engine performance was smooth and powerful, and no fault codes returned. Mercedes 722.6 transmissions are pretty durable mechanically. However, the Achilles heel of the 722.6 is the conductor plate coupler. See figure 2a, red circle, shown disconnected from the transmission.
The conductor plate coupler provides the connection to the wiring harness for the transmission control module. See figure 2b, black box.
The issue with the conductor plate coupler is that it is prone to leaking. The transmission fluid leaks into the coupler and creates electrical shorts. This situation can cause check engine MIL, irregular shifting, limp mode, or damage to the transmission control module.
In some cases, the transmission fluid can leak all the way up to the transmission control module through approximately three feet of wiring. See figure 2b, red circle, transmission fluid leakage.
As is the case with many European automobiles, Mercedes has very sensitive electronics. Electrical shorts or spikes can "zap" out a control module in no time. Even though fuses are in place to protect the electrical components, they don't always react quickly enough. It’s common to find a "zapped" out module and all fuses in perfect condition.
The BMW E46 3-series model uses two separate fuel tanks. The fuel system uses a jet system to transfer fuel from the left tank to the right tank. When fuel level irregularities come about, our BMW technician can access the amount of fuel in each tank via instrument cluster. See the red-circled area in Figure 3a. The first three digits (015) is the amount of fuel in liters in the left tank. The last three digits (327) is the amount of fuel in liters in the right tank. 1.5 liters plus 32.7 liters is equal to 34.2 liters. The fuel capacity for the E46 model is 63 liters, 34.2 liters is equal to slightly more than ½ the fuel capacity. Notice the fuel gauge in Figure 3a; the needle is slightly past the half mark, so this fuel gauge is reading accurately.
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