Smart Roadster Transmission Fails with Grinding & Limp Mode

Had similar symptoms on a Smart ForTwo from 2006. The transmission fault warning appeared suddenly during highway driving, followed by rough shifts and concerning noises. The car went into limp mode as a safety measure. The issue turned out more serious than expected. The transmission oil sensor was reporting incorrect readings, but this masked a bigger problem. The actual oil level was critically low due to a slow leak from a damaged seal. This caused insufficient pressure in the transmission system. The repair required: Replacing the faulty transmission sensor, Fixing the leaking transmission seal, Complete transmission oil flush and refill, Recalibration of the transmission control unit This combination of issues could have caused major transmission damage if left unchecked. The oil pressure was dangerously low, risking internal component failure. Based on your symptoms and the sudden onset, recommend getting it checked immediately. Watch for metal particles in the transmission oil, this would indicate internal wear has already started. Do not drive the car more than necessary until repaired, as low oil pressure can quickly lead to transmission failure.

Thanks for sharing that detailed experience. Your symptoms sound exactly like what happened to my Smart Roadster last summer. After replacing the pressure sensor, my mechanic found the real issue was a worn transmission seal causing pressure loss. The pressure switch readings were incorrect due to this underlying problem. Did you remember roughly what you paid for the complete fix? Also curious if you had any transmission issues since the repair was done. My transmission fault warning never came back after the fix, but always good to hear long-term experiences.

Thanks for asking about the costs. Since having the transmission oil pressure sensor and oil level fixed last summer, I have not experienced any more transmission issues. The full repair came to 365€, which included replacing the faulty pressure switch, fixing the low gearbox oil level, and doing a thorough check of the transmission system. The repair has proven reliable, no warning lights or strange noises since then. The transmission shifts smoothly now and the car runs perfectly. Looking back, catching the oil pressure sensor fault early likely prevented more extensive transmission damage and higher repair costs. The mechanic did a proper job addressing both the sensor and the underlying oil level problem. Regular transmission maintenance really pays off in preventing these kinds of pressure sensor and oil level issues from developing again. The transmission system has been problem-free for thousands of kilometers now.

Thanks for all the helpful feedback. Finally went to get it checked last week. The mechanic found both a faulty transmission pressure sensor and a slow leak from a worn seal, just like you described. Total repair cost was 425€ including parts and labor. The pressure sensor was sending incorrect readings to the transmission control unit, while the seal leak had slowly reduced the oil level. Had to wait 2 days for the parts but the repair went smoothly. The mechanic did a full transmission oil flush and checked thoroughly for any metal particles. Been driving for a week now and the transmission shifts perfectly again. No more warning lights or strange noises. Really glad I caught it early before the low oil pressure could cause serious transmission damage. Lesson learned about getting these transmission issues checked out quickly when they first appear.