BMW Intermittent Warning Lights and Fail Safe Mode
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When warmed up, a BMW may show warning lights on the instrument cluster and even go into fail-safe mode. The warning lights may come up intermittently. The vehicle returns to regular operation after the car is restarted or cooled down. This guide will discuss common issues that can cause intermittent BMW problems.
At a Glance
- Pattern: Warning lights or limp mode once warm, back to normal after a restart or cool down
- Check first: Battery condition and charging voltage; low voltage causes random faults
- Common causes: Transmission module (EGS), engine module (DME/DDE), gear selector, sensors, low transmission fluid, wiring or CAN bus faults
- Next step: Read codes from all modules, not just the engine
- Tip: Note when the fault happens (hot, cold, over bumps) to narrow it down
Symptoms
- Intermittent loss of power
- ABS / Brake / Traction Control light on
- The transmission won’t change gears.
- Stuck in fail-safe/limp mode
- Random warning lights on the dash
- Intermittent warning lights
Typically, allowing the car to cool down, restarting it, or clearing the codes will enable the vehicle to run normally.
A BMW can get stuck in gear intermittently when the transmission fluid is low or the onboard voltage drops while the engine runs. If you have a BMW that loses power and gets stuck in gear (fail-safe mode), you must first check the transmission fluid level and ensure a good battery with a reasonable charge.
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If the transmission fluid level is correct, the next troubleshooting step is to read the fault codes from all modules.
Possible Causes
- Gear selector
- Transmission control module (EGS)
- Engine control module (DME / DDE )
- Weak battery
- Requires DME / EGS software update
- Faulty temperature sensor
- Low transmission fluid level
- Engine temperature sensor
- ABS faults
Any of these modules could have an internal fault. A defective connector or damaged wire harness can also be a problem. The problem can also be a fault in the CAN bus network. The typical modules on the CAN-BUS II are the gear selector, engine control unit, and transmission control module. The next step is to read the codes from all the modules listed above.
How to diagnose BMW intermittent problems
The next step in diagnosing BMW’s intermittent issues is to read the fault codes from all the modules and determine the next steps. You will need a scanner that can read all BMW modules, not just the engine,’ fault codes.
The YOUCANIC UCAN-II Pro can read, and clear fault codes in the engine and other control modules on supported vehicles, just like any professional scanner.
- Locate the diagnostic port under the dashboard.
- Plug in your scanner.
- Turn on the ignition and your BMW scanner.
- Select your BMW model.
- Select to run a full system scan. Depending on the scanner, it will show as Health Report, Full Scan, or Quick Scan.
- Analyze all the fault codes that show as current or intermittent.
After reading the code, you should better understand what to focus on next.
Intermittent Codes
A BMW with the following fault codes may have a bad engine control unit, shifter module, or transmission control module. The most likely cause is a faulty transmission control module, which in most BMWs is installed inside the transmission on the valve body.
DME / DDE Engine Codes
- CD950F: No message request torque crankshaft transmission 2 0xA0, receiver DME/DDE, transmitter EGS
- CD94ED: No message data display transmission, 0x3FD, receiver DME / DDE, transmitter EGS
- CD94DC: Electronic transmission control EGS, PT CAN, PT-CAN2, Communication Fault
- CD94C3: No message diagnostic OBD transmission, 0x396, receiver DME / DDE transmitter EGS
- CD94BA: No message, display, engine speed, dynamization, receiver DME / DDE/ EGS transmitter
- CD9487: No message request torque crankshaft, transmission, receiver DME / DDE, transmitter EGS
- CD946B: No message status transmission control unit, receiver DME / DDE, transmitter EGS.
- CD9469 Message, status transmission control unit, signal invalid.
EGS Transmission Codes
- 4209A4: Temperature sensor, Hotmode 3 excess temperature with possible damage to transmission coolant line detected.
- CF047F: EGS, PT-CAN2 Communication Fault
- CD1701: Signal gear selector switch status, total communication failure, invalid transmitter GWS.
- CF17A1: No message status, gear selector switch, receive EGS, transmitter GWs.
- CF17B1: No message status, gear selector switch, receiver EGS, transmitter GWS
It is important to note that BMW’s irregular fault codes can be very challenging to diagnose. We do not recommend replacing any of the parts or components listed here without first performing a diagnostic.
Check these troubleshooting and repair guides for more help on your BMW.
Frequently Asked Questions
Why does my BMW go into limp mode and then work after a restart?
An intermittent fault, often from low voltage, a heat sensitive module or sensor, or a wiring problem, triggers fail safe mode. Restarting resets it until the fault returns.
Can a weak battery cause random BMW warning lights?
Yes. Low voltage while driving can set faults in several modules at once and cause random warning lights.
Which modules should I scan?
Read codes from the transmission (EGS), engine (DME or DDE), gear selector and ABS modules at minimum.
Can low transmission fluid cause a BMW to get stuck in gear?
Yes. Low fluid can cause the transmission to go into fail safe mode and stay in one gear.
Related Guides
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- BMW Hood Open Warning on Dashboard
- BMW Engine Oil Level Low Below Minimum Warning
- BMW Failed ATE MK60E ABS Module May Trigger ABS and DTC Lights
