It’s been a while since I’ve mentioned hybrid vehicles in this column (click HERE for a review), so I thought I’d bring them back today! In the past we’ve discussed the basics of hybrid system operation and a few specific operations related to the Toyota Prius.
Although we have significant growth in the hybrid vehicle market, the Prius is still, by far, the most prolific hybrid vehicle on the road. In light of the upcoming winter season (yes, I said it: the ‘w’ word!) today’s column will discuss:
- Making the Prius internal combustion engine (IC) run continuously while performing diagnostics.
- Servicing the coolant heat storage tank and associated components.
Prius - Inspection Mode
Inspection Mode is an operating mode that allows the Prius IC engine to run continuously even if the vehicle is not moving. Official state inspection procedures may require the engine to run and this can be accomplished with Inspection Mode. You may also require the engine to run while performing certain diagnostic operations such as inspecting the CKP or CMP signals.
During normal operation, the IC engine is controlled by the Hybrid Vehicle Electronic Control Unit (HV ECU), and the engine may or may not run when in Ready Mode and the vehicle is not in motion. Inspection Mode commands the engine to run continuously.
Inspection Mode can be enabled with or without the Toyota scan tool (Techstream). The following describes how to enter Inspection Mode without a scan tool:
- Engine should be warm, set parking brake, gear selector in P, and A/C OFF.
- Turn ignition ON (READY lamp illuminated), then turn ignition OFF.
- Perform the following steps within 60 seconds.
- DO NOT depress the brake pedal. Press and release the Power button twice to enter IG-ON.
- Fully depress and release the accelerator pedal 2x with the gear selector in P position.
- Depress the brake pedal and move the gear selector to N position.
- Fully depress and release the accelerator pedal 2x with the gear selector in N position.
- Depress the brake pedal and move the gear selector back to P position.
- Fully depress and release the accelerator pedal 2x with the gear selector in P position.
- The hybrid system warning on the multi-function display should flash.
- Depress the brake pedal and depress and release the Power button once to turn ignition ON (READY lamp illuminated).
- The IC engine should start and run continuously.
When in Inspection Mode, engine speed depends on accelerator pedal position:
- Accelerator pedal not depressed: idle (approx. 1000 rpm)
- Accelerator pedal depressed <60%: approx. 1500 rpm
- Accelerator pedal depressed >60%: approx. 2250 rpm
Alternative to Inspection Mode: There is another way that technicians commonly use to force the Prius IC engine to run continuously. Although this method does not permit the engine to idle, it can be used to quickly command the engine to run:
- Set parking brake, gear selector in P, and A/C OFF.
- Turn ignition ON (READY lamp illuminated).
- With gear selector in P, simply depress the accelerator pedal.
The engine will run continuously as long as the pedal is depressed. Releasing the pedal usually causes the engine to stop.This method can be used during diagnostics, provided you have a second person to run the accelerator pedal!
Coolant Heat Storage Tank
A component that is unique to the Prius, and one that commonly requires service for a number of reasons, is the coolant heat storage tank electric pump. The 2004-2009 Prius models have the coolant heat storage tank in the right front fender and as such it is prone to damage from even minor front end collisions. Among other things that can go wrong, the tank has an electric pump that can become noisy.
Note: There is actually a Technical Service Bulletin (TSB) from Toyota for replacement of a noisy pump. The TSB number is: T-SB-0087-08.
The Prius engine cooling system is more complex than most vehicles. In addition to the engine-driven coolant pump, there are two electric coolant pumps and an electrically operated rotary coolant flow control valve. When servicing this system there are a few important things to remember:
- The coolant is kept at a temperature of 180 degrees Fahrenheit for up to three days after the vehicle has been shut off.
- Refilling the cooling system requires more work than a conventional cooling system.
- The hybrid inverter utilizes a separate cooling system from the engine cooling system.
The following are some of the service precautions to be aware of when servicing the Prius cooling system as laid out by Toyota:
Toyota service information (TIS) specifies that the coolant heat storage tank pump connector be disconnected when draining engine coolant. This is done to prevent the electric pump from running when the system is empty. Disconnecting this pump may cause a DTC to set and the Malfunction Indicator Lamp (MIL) to illuminate.
If a DTC is set and the MIL illuminates after engine coolant drain and refill, use a Techstream scan tool or equivalent to clear the DTC.
Refilling and bleeding air from the Prius engine cooling system after draining can be challenging. Toyota service information (TIS) specifies a procedure that uses the Techstream scan tool or equivalent to run the electric coolant pump. The engine must experience several heating and cooling cycles while the system is bled. This can be time consuming but not being diligent about the bleeding procedure can result in an unhappy customer at best, and a catastrophic engine failure at worst!
An alternative method for refilling the engine cooling system uses a cooling system vacuum fill tool. One brand on the market is called AirLift. When powered by a shop air supply, the tool creates a vacuum that will remove most air from the cooling system. Large diameter radiator hoses may collapse during this process. Closing one valve on the tool and opening a second valve allows atmospheric pressure to push coolant from a supply bottle into the cooling system.
A system refilled this way often fills completely and requires no bleeding. Most technicians prefer using this tool over the factory fill procedure. Many have even taken to using a vacuum fill tool on all the vehicles they service.
The 2010 Prius does not use an engine-driven coolant pump. The 2ZR-FXE engine in this model has an electric coolant pump. The pump uses a brushless-type DC motor controlled by the ECM. On the Toyota Techstream scan tool, this pump is displayed as Coolant Pump B.
There is no crankshaft-driven belt on this engine since all of the accessories that are normally belt-driven are electric (power steering, A/C, coolant pump, alternator, etc.). I’m betting that you’re going to see these systems begin to pop up on non-hybrid systems as well!
That’s it for today! Keep up the great work and never stop learning! As always, and as some of you have done, I can be reached through Examiner.com or at www.intelligentmechanic.com. Enjoy the Labor Day weekend and keep it safe!
