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SOLVED P1151 Coolant Heat Storage Tank

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by awommy, May 3, 2015.

  1. awommy

    awommy Junior Member

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    My MIL has been intermittently showing up, and I'm pulling DTC P1151 - Coolant Heat Storage Tank. This is the only DTC that I'm getting. I have recently replaced the Coolant Control Valve, as I had been getting a P1121, and attempted to refill the coolant myself.

    From what I have found so far, it looks like there's a possibility that I didn't properly bleed the system of air while refilling the coolant. I've attempted to bleed more out, but I'm only getting coolant coming out of the bleeder, so I'm not sure that this is the issue. I have taken it to the dealership, and they noted that this tank is damaged, and the water pump will also need to be replaced.

    So my question is, will replacing the Heat Storage Tank resolve the P1151 issue? From what I've seen in the attached document, the storage tank is just an insulated container; it doesn't seem to have any functioning pieces, which makes me question whether replacing this will actually resolve the issue...
    If replacing the tank is not going to resolve the problem, where else should I look for a potential resolution? Could the water pump be a potential source of the problem?
     

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  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    When you were bleeding air out of the engine coolant system, did you also run the coolant heat recovery system pump to move coolant into the CHRS heat storage tank? If there is any doubt whether air remains in the CHRS part of the system, I suggest you work on that first.

    Assuming there is no air present, then replacing the heat storage tank should resolve the P1151 issue. Normally this tank is not reported to fail unless the car was in an accident impacting the left front fender, behind which the tank is mounted.
     
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  3. awommy

    awommy Junior Member

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    Well, I just removed the tank to inspect it, see if there's any obvious damage or blockage in the hoses, which meant draining the coolant again. The tank is pretty damaged; no leaks, but it got crunched pretty good. The car had been in a couple of accidents before I purchased it, so I'm going to assume that this is one section that got hit. There's a number of other signs that indicate this as well.

    I do not know what the coolant heat recovery system pump is...To help purge the air, I had the bleeder valve opened. I would put the car in inspection mode for a few moments, to get the pump going, then turn it off and let things settle and cool down, then massaged the hoses I could wrap my hands around. I did that a few times, until I couldn't add any more coolant. Is there more that I could do to purge more air from the system?

    I'm guessing that the tank will need to be replaced. Like I said, it's pretty well beat up. I just don't really understand how the ECM can know that it's damaged, as it's not really a function part, as much as a passive storage tank...
     
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The CHRS system stores hot engine coolant in the tank that you inspected. The concept is that when the engine is next restarted, the CHRS pump will flow the ~3 liters of hot coolant into the engine, thus speeding up the engine warmup cycle. If the engine warms up faster, it will reach its normal efficiency level faster and exhaust emissions are correspondingly reduced. This qualifies the 2G Prius for AT-PZEV certification by the California Air Resources Board.

    Now, your question about how the engine ECU knows the tank is not doing its job: ~5 hours after the car is shut down, the engine ECU will run the CHRS pump for a brief period so that some of the hot coolant will flow out. A sensor at the tank output registers the fluid temperature. If the temperature has dropped more than 30 degrees C (compared to the temp of the fluid entering the tank 5 hours prior) then the engine ECU will determine the tank has failed and log the DTC you retrieved.

    I have posted on how to replace 2G engine coolant. Prior to Mini VCI becoming easily available, my method was to remove the CHRS relay and short the switched relay terminals at the socket to run the pump for brief periods. Now that anyone can buy Mini VCI and have the same diagnostic power as a Toyota dealer tech using Techstream, you can use that software to control the CHRS pump instead of playing around with the CHRS relay socket.
     
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  5. awommy

    awommy Junior Member

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    Okay, great. I found a post you wrote about changing the engine coolant, in which you mentioned how to short the switched relay terminals:
    Changing engine coolant | Page 2 | PriusChat
    I gave that a shot just now, and was able to add about another quart (possibly also due to cooler temps outside, now that it's night, and a couple of hours since the car was last turned off). I will continue to check periodically that it's full, but I guess I'll be doing this again in the next week or so once I can get a replacement tank. Thank you for your help! I will update on the P1151 code once I replace the tank.
     
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  6. awommy

    awommy Junior Member

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    Realized I never completed this thread. I ended up replacing the whole CHRS tank, and that did solve the problem. Thank you for your help Patrick.
     
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