Hello Fellow Prius Owners, I am the original owner of a 2005 Prius that now has about 108,000 miles on it. Recently I have heard a revving noise coming from my engine while coasting down a mountain on my commute home. I have not seen any warning lights telling me something is bad. Any ideas on what could be causing this or what may be going bad in the near future?? Thanks.
Hi plaineater, do you have all the green bars showing on your battery charge (SOC) indicator when this happens? If so then the issue is almost certainly the managment computer dumping charge by spinning the engine. This is normal behavior when the battery has too much charge and you're still trying to regeneratively brake down a big hill. BTW. Here the engine is just being used as a load (like a big compression brake) to give the electric motor something to dump excess energy into. If this is happening a lot more than it used to then it could indicate that your traction battery is starting to lose it's capacity. It might not be a problem though, as long as the SOC doesn't rise and fall excessively rapidly. Have you noticed any other SOC issues?
Uart has it right. It's normal engine braking, just like B mode but automatic. The only reason for concern is if it didn't used to do this on the same drive, in which case the traction battery is starting to show a loss of capacity. Tom
Yep to uart's comments. If one has a ScanGauge, when going down the hill at <42 mph at the HV battery's state of charge hits 80% (which is shown has a full indication w/all green bars on the MFD), then the gas engine will kick on and can even hit 3000+ rpm. One will also see no regen happening instead power being drawn from the pack (BTA X-Guage on ScanGuage). In non-battery too full conditions, if one just coasts, one sees ~15-20 amps of regen rather than a drain.
