muz84

I have kind of weird problem with my RX400H 2007. When I turn my air con on, I get Check Hybrid and Check VSC message displayed with check engine light, traction light and red triangle. Scanning tool displays P010A code (Mass Air Flow (MAF) B Circuit Malfunction). Just to make sure, I ran vehicle for about a month without turning on A/C (blower was on most of the time) and no errors. When I turned on A/C today, same error came up. I’m unable to understand what air con and MAF circuit to do with each other. The vehicle keeps running fine when errors come but doesn’t start again after turning off, until code is cleared or battery terminal is removed and replaced. I’ll really appreciate if anyone can help me solve the issue.

mnewxcv

One thing worth noting is the ac compressor on the rx400h is a high voltage compressor which gets power directly from the hybrid battery, unlike traditional vehicles which use a belt driven compressor. Also, I don't know if you've ever had your ac system serviced, but it uses a special refrigerant that is non conductive because of the high voltage. I don't see how the two systems could be connected but I will see if I can dig up some schematics.

muz84

Thanks for reply and thanks in advance for digging up schematics. I owned vehicle for over 2 years and never had ac serviced. The issue came up just recently.

About a year ago I replaced spark plugs, retorqued valve cover, replaced plenum and upper intake gaskets, replaced PCV valve, replaced radiator and coolant, cleaned MAF sensor using CRC MAF cleaner and replaced air filter. Vehicle kept running fine for about a year after that without any issues.

mnewxcv

That is the connector that plugs into your Mass Airflow Sensor.

With ignition on, pin 1 should have 9-14v. Check with and without AC on.
Pin 2 should have less than 1 ohm resistance to ground. Check with and without AC on.
With ignition on, pin 3 should have greater than 10k ohms resistance to ground. Check with and without AC on.
With engine running, measure voltage between pins 2 and 3. Should be 0.5v - 3.0v.

Both the MAF and the compressor connect to the Hybrid Vehicle (HV) Control ECU, though not on the same harness connector. It is possible there is a fault within the HV ECU, ECM (within HV ECU), wiring harness, or connector. You seem to have narrowed it down to only happening with the AC on, but it still doesn't hurt to clean your MAF if it is dirty. If you are able to measure the things listed above, we can further troubleshoot.

muz84

Great. I’ll try to do this over the weekend and will let you know the findings. Thanks for your help.

muz84

I managed to do the measurements today and the results are:

Ignition on, AC off:
Pin 1 to ground: 11.61v (battery was pretty low)
Pin 2 to ground: 423 ohms
Pin 3 to ground: 325k ohms

Ignition on, AC on:
Pin 1 to ground: 11.49v
Pin 2 to ground: 485 ohms
Pin 3 to ground: 344k ohms

Engine running:
Pin 2 & 3 voltage difference: zero (stayed zero with ac on)

Please let me know your thoughts. Thanks for the help.

mnewxcv

Not much changes when turning the AC on it looks like, which is weird that turning it on is what makes the warning light come on. That being said, pin 2 should be essentially 0 resistance to ground, and you have 423 ohms. Is there any corrosion on the pins? Another thing you can check is the voltage on pin 3 when measured to ground. Pin 2 *should* be ground, but in this case it isn't, so measure pin 3 to ground and see if you get the 0.5v - 3.0v range. Again, do this with the engine running, not just with the car in the ON position. Not entirely sure if it makes a difference, but manual states engine running.

Now regarding pin 2. Pins 2 and 3 connect to the H32 connector of the Hybrid Vehicle Control ECU. You can measure the voltage between 2 points on the connector at the ECU like you did for pins 2 and 3 of the MAF connector. If you still have no difference (no voltage/no ground), it is likely an ECU issue. If there is a difference and the measurement is good, the problem appears to be with the harness or connector.

Image attached, may need to save and enlarge to see the location of the pins.

• Start the engine.
• Measure the voltage between terminals VG and EVG of the H32 HV control ECU connector.
  
  Standard voltage
  
  
  Tester ConnectionConditionSpecified Condition
  
  VG (H32-30) - EVG (H32-29)
  
  Engine idling
  
  0.5 to 3.0 V

mnewxcv

location of HV ECU






The glove compartment assembly should have 2 screws and 2 bolts holding it in place.

muz84

I managed to measure voltage of pin 3 to ground and was 0.2v when engine not running and 0.1v when engine running. Exactly same for pin 2. I also measured voltage of pin 4 to ground and it was 4.98v when engine running (not sure if its relevant). No corrosion on pins that I can see.

I could not remove the glove compartment as I could see screws but no bolts. Will figure that out soon.

In worst case if it’s an ECU issue, does that mean I will have to replace the ECU? Is it quite expensive?

mnewxcv

Here is a picture showing the location of the screws and bolts:

mnewxcv

You may need to remove a cover below the glove box to see the bottom hardware.

As for the hybrid ECU, I see them on EBAY in the neighborhood of $100 used, though I do not know anything about swapping ECUs, and you may need to go to the dealer to have the new ECU 'paired' to the car and other ECUs. I just can't say for sure.


edit: I did find this:

7. ECU COMMUNICATION ID REGISTRATION
NOTICE:
The ECU communication ID should be registered when the hybrid vehicle control ECU is replaced
in order to match the HYBRID VEHICLE CONTROL ECU COMMUNICATION ID.
The hybrid vehicle control system cannot be started unless the HYBRID VEHICLE CONTROL

ECU COMMUNICATION ID matches.

Insert already registered master key in key slot and turn power switch ON (READY) with brake pedal depressed.

Check that hybrid control system stays on for more than 3 seconds.


so seems like replacing the HV control ECU isn't a very big deal if necessary. However, it may be difficult to find one with the same part number as there were many.

muz84

Thanks for the great support. After doing whatever I could do, I took vehicle to dealer. The fault code my obd reader was reading turned out to be wrong. The actual fault code reported by techstream is P0AA6 High voltage insulation fault. So your initial suspicion could be right. Dealer believe the A/C compressor causing short circuit due to wrong oil. I have not replaced oil or refrigerant in last 2 years since I owned the vehicle. Is there anything I can try before following their very costly recommendation to replace the A/C compressor and flush out the system?

Diagnosis data including Freeze frame data and short wave graph is attached.


Diagnosis P0AA6

Freeze Frame data pg 1

Freeze Frame data pg 2


Health check

muz84

I once washed off the engine block and top of compressor with garden hose followed by degreaser spray (due to oil leak). Could that cause rust in high voltage connection on compressor? Is it safe to unplug that to have a look, after disconnecting 12v battery? Is it easy to disconnect without special tool?

mnewxcv

Do not touch the orange lines or connectors. They are high voltage and still live with the 12v battery disconnected. I will look into that fault code and see what I can find.