Peugeot 406 Limp Mode ABS Fault

I had a similar issue with my 2008 Volvo XC70. It also went into a 'limp home' mode with erratic shifting. In my case, it turned out that a faulty wheel speed sensor was sending incorrect data to the traction control system, which then affected the transmission control module (TCM). The TCM, interpreting this data, limited engine power and gear selection to protect the drivetrain. ABS, traction control, and the gearbox are often linked via the CAN bus, so faults can cascade. Did your diagnostic check the ABS sensors?

That's interesting about the Volvo. The ABS sensors were checked, and no immediate faults were detected, but the diagnostic tool did flag some historical inconsistencies. Could intermittent or marginal sensor readings still cause such a problem, even if they don't trigger a persistent error code?

Yes, absolutely. Intermittent faults are the worst to diagnose. Even if the ABS sensor readings appear within range at any given moment, a brief drop-out or spike can confuse the control module and trigger the limp mode. The system may not register a hard fault, but the erratic data can still disrupt communication between modules. Given the age of your 406 and the mileage, a sensor could be on its way out. I would advise a workshop visit.

Understood. I appreciate the insight regarding intermittent sensor faults and their potential impact. That confirms my suspicions. I will bring it to a trusted mechanic for further diagnosis and component testing. Eventually, no costs were involved, as a connector simply had to be cleaned.