Experiencing a frustrating issue with a 1999 BMW 528i 2.8L (E39 generation)? Many owners encounter a situation where their vehicle seems to run perfectly fine – it starts, idles, and drives without apparent problems – yet refuses to communicate with any OBD2 scan tools. This article delves into a troubleshooting journey on a ’99 BMW 528i exhibiting exactly this symptom: a misfire and a complete lack of communication through both the standard 16-pin OBD2 port and the under-hood 20-pin diagnostic connector.
The vehicle in question is a 1999 BMW 528i, equipped with the 2.8L DOHC M52 TU engine and the base instrument cluster (without IKE). Despite the engine running, a persistent misfire is present. More critically, attempts to connect with the car’s computer system via diagnostic tools have been unsuccessful. This lack of communication prevents proper diagnosis and repair of the misfire and any other potential underlying issues.
Several diagnostic steps have already been undertaken to pinpoint the cause of this communication failure. Initially, all fuses in both the glove box and the trunk power distribution box were checked and confirmed to be in good working order. To rule out issues with the scan tools themselves, three different OBD2 scanners were tested on the 16-pin OBD2 connector, all failing to establish communication with the DME (Digital Motor Electronics), BMW’s engine control unit. Furthermore, a Mac Mentor (generation 3) professional scan tool was used on the 20-pin diagnostic connector under the hood. Attempts were made using both generic OBD2 protocols and enhanced, manufacturer-specific BMW protocols, but again, no communication could be established.
Further investigation into the 20-pin connector revealed an anomaly. Pin 2, expected to provide power, does show a 12V reading upon starting the car. However, this voltage drops to 0V after approximately 10 seconds, which could indicate a power supply issue or a control module shutting down.
To examine the vehicle’s communication networks, the CAN bus (Controller Area Network bus), responsible for communication between the transmission control module and the DME, was analyzed. Using an oscilloscope at the DME (pins 3 and 4 of connector X60002), the CAN H and CAN L voltages were measured and found to be within expected ranges and mirroring each other, suggesting the CAN bus itself is likely functioning.
Next, the diagnostic bus (D-bus), specifically pin 7 of the 16-pin OBD2 connector, was examined. A graphing multimeter showed a consistent 12V at idle. However, when a scan tool was connected to the 16-pin connector and attempted to initiate communication, the voltage on pin 7 fluctuated between 12V and 0V briefly before returning to a steady 12V. This fluctuation, followed by a communication failure message (“make sure ignition is on and scan tool is properly connected”), suggests an issue with the diagnostic communication line itself or the DME’s ability to respond.
As a potential troubleshooting step, the IKE (Instrument Kombi Elektronik) module, which serves as a gateway module in some BMW systems, was disconnected. Despite disconnecting the IKE, communication with the DME via pin 7 of the OBD2 connector remained impossible.
Based on these diagnostic steps and the persistent lack of OBD2 communication, the primary suspicion points towards a faulty DME. The inability to communicate with the DME through multiple scan tools and diagnostic connectors, even after checking power supplies and communication bus lines, strongly suggests an internal failure within the DME itself. While the engine runs, critical diagnostic functions appear to be offline due to this suspected DME issue.
While DME replacement is a significant step, it is currently the most probable solution given the symptoms and troubleshooting results. Further input and shared experiences from other BMW technicians and enthusiasts are highly welcomed to confirm this diagnosis or suggest alternative troubleshooting paths before proceeding with a DME replacement. Has anyone encountered a similar no-communication issue on a ’99 BMW 528i where everything else seems to function correctly? Any insights or additional diagnostic steps would be greatly appreciated.
