Service Guys Clueless on error P0128 - Toyota Yaris Forums

CoryM · 06-23-2015, 11:51 PM

P0128 means the computer is seeing coolant temps below the minimum (whether it is or not). 99% of the time this means the thermostat is stuck open, and the engine warms up too slowly. Tsats sometimes act up intermittently, so I don't blame them for starting with a Tsat even if it tested out OK in the shop. It's step 1 for sure. Since it seems the Tstat is not the problem, now it gets a little harder (especially since it isn't happening all the time). It could be: faulty sensor/wiring, faulty ECU, faulty ECU software, low coolant (leak), incorrectly mixed coolant, waterpump not circulating and a few other things. I know it's frustrating as a customer, but unless the problem happens quickly so you can test it while it's acting up, it can be very tough to diagnose.

I am not sure what "cord" they are mentioning. If you could get a better description, I may be able to advise further. $1200 goes a long way on a Yaris so I am curious what they are wanting to do. Possibly a wiring harness?

Cheers.

Thread Tools
Show Printable Version Email this Page
Display Modes
Switch to Linear Mode Switch to Hybrid Mode Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
2007 Yaris and Service Engine Soon	takissd	DIY / Maintenance / Service	8	06-02-2011 04:18 PM
Previa service + yaris update	jetlag 5000	General Yaris / Vitz Discussion	0	10-17-2010 03:53 AM
I hate cable service providers.	Altitude	Off-topic / Other Cars / Everything else Discussions	27	09-12-2010 10:09 AM
service maintance light	io3	Yaris TS Talk	11	09-22-2009 04:03 PM
Why does 15000 service cost so much more than 5000 and 10000 mile service?	monyaris	DIY / Maintenance / Service	7	06-25-2009 08:12 PM

06-23-2015, 11:51 PM	#2
CoryM Drives: 2009 5-door, 5-speed Join Date: Sep 2011 Location: White Rock BC Posts: 687	P0128 means the computer is seeing coolant temps below the minimum (whether it is or not). 99% of the time this means the thermostat is stuck open, and the engine warms up too slowly. Tsats sometimes act up intermittently, so I don't blame them for starting with a Tsat even if it tested out OK in the shop. It's step 1 for sure. Since it seems the Tstat is not the problem, now it gets a little harder (especially since it isn't happening all the time). It could be: faulty sensor/wiring, faulty ECU, faulty ECU software, low coolant (leak), incorrectly mixed coolant, waterpump not circulating and a few other things. I know it's frustrating as a customer, but unless the problem happens quickly so you can test it while it's acting up, it can be very tough to diagnose. I am not sure what "cord" they are mentioning. If you could get a better description, I may be able to advise further. $1200 goes a long way on a Yaris so I am curious what they are wanting to do. Possibly a wiring harness? Cheers.