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Genchi Genbutsu
Genchi Genbutsu, Toyota Master Technician
Category: Toyota
Satisfied Customers: 4387
Experience:  Toyota Certified Master Diagnostic Technician, ASE Master Technician with L1 Advanced Engine
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When I turn the key on the 4LO light starts flashing

Customer Question

***** *****, When I turn the key on the 4LO light starts flashing and the check engine light comes on
JA: Thanks. Can you give me any more details about your issue?
Customer: my vehicle is a 2010 Tundra 4x4 with 5.7L I started the vehicle but the condition did not go away so I shut it off
JA: OK got it. Last thing — Toyota Mechanics generally expect a deposit of about $20 to help with your type of question (you only pay if satisfied). Now I'm going to take you to a page to place a secure deposit with JustAnswer. Don't worry, this chat is saved. After that, we will finish helping you.
Submitted: 7 months ago.
Category: Toyota
Expert:  Genchi Genbutsu replied 7 months ago.
Thank you for allowing me to help you with this concern today and am sorry to hear that this is happening. I will have to ask you a few questions so that I can get a better understanding as to what may be going on with your Tundra.Have you had a chance to pull codes yet?How many miles are on your Tundra?
Customer: replied 7 months ago.
I have not pulled codes as I did not want to drive the vehicle without knowing if I would damage anything by driving it.
This is my wife's truck that she uses to pull a two horse trailer and not often - it has 18,000 miles on it.
Expert:  Genchi Genbutsu replied 7 months ago.
Only 18,000 miles? That's a low mileage Tundra. :)The reason I was asking about speed mph and if you pulled codes is because what we see quite often is that the AIP (Air Injection Pumps) will go out and cause this exact condition. Here is an article describing the extended warranty Toyota issued on this.and here is the bulletin that covers it for 10 years or 150,000 milesDoes this make sense?If you have more questions, please ask as I strive to give Excellent service. Also please take the time to rate my help (1-5 stars), as it helps me.
Customer: replied 7 months ago.
I guess I am really confused how you narrowed it down to the air injection pump (AIP) issue. I know I am not a Toyota mechanic but I think logically as an engineer. Why would the 4LO light flash? I understand the engine check light would come on for an AIP issue but a flashing 4LO light would appear more related to ECM (PCM) which the check engine light would also come on. Either way, with your experience would the vehicle be safe to drive (30+ miles to the dealership), have it towed to the dealership, or drive to O'Reilly's which is the nearest code check at 14 miles?
Expert:  Genchi Genbutsu replied 7 months ago.
but I think logically as an engineer. So do I and most Technicians... :)Just for a quick second on the 4WD low light flash, were you using the 4WD when this happened?
Expert:  Genchi Genbutsu replied 7 months ago.
Were you able to see my last reply?
Customer: replied 7 months ago.
I am at work that is why I am slow to respond.
No, was not using the 4WD the vehicle was mot moving. It was sitting in the garage. I started it to move it out so I could work on another vehicle when the flashing 4LO and check engine came on. I did remove and put back on the negative battery cable to see if that would clear/reset the problem.
Expert:  Genchi Genbutsu replied 7 months ago.
I am at work that is why I am slow to respond.Oh, I apologize for the intrusion then. Don't mean to sound rude and am here to help when needed. I know I am not a Toyota mechanic but I think logically as an engineer. Why would the 4LO light flash? I understand the engine check light would come on for an AIP issue but a flashing 4LO light would appear more related to ECM (PCM) which the check engine light would also come on.My experience is why... :) "No, was not using the 4WD the vehicle was mot moving."See. There is no logical reason why the 4Lo light should be on but the software engineers just designed it that way. My personal thinking is that I know all these computers "talk" via the CAN (Control Area Network) BUS to each other and on many models like this one, will 'tattle tell' on each other when they see one system having a problem. They see the problem on another system and then turn their own warning light on and set a code for not being able to communicate with that ECU. I hope that made sense.If you were to pull codes from the 4WD ECU, they would just be codes for non communication with the Engine ECU, again it's just 'tattle telling' on the ECU having the problem. I did remove and put back on the negative battery cable to see if that would clear/reset the problem.Did that help? In some cases it will till the problem happens again.
Customer: replied 7 months ago.
No, removing the cable did nothing.
Expert:  Genchi Genbutsu replied 7 months ago.
Ok, them clearing the codes may work but again, that would be until the problem happened again.Are you within the 10year/150,000 mile limit?
Customer: replied 7 months ago.
I have to go to a meeting so must sign off. Thank you for your help! I am still baffled since it was parked without any issues, then turned on the key and issues appeared. Has there been issues with moisture in any sensors? Yes, it is in the 10year/150,000 limit. I think I will have to get it towed to the dealership.
Expert:  Genchi Genbutsu replied 7 months ago.
I have to go to a meeting so must sign off.Ok. Has there been issues with moisture in any sensors? Yes, that is what Toyota says is happening and why they added a heating element on the newer ones. To prevent moisture build-up. Yes, it is in the 10year/150,000 limit. I think I will have to get it towed to the dealership. I think that is best because it will be fixed without you spending any money on this repair. Also, if needed, Toyota will cover the cost of the tow. Just call your Toyota Dealer and tell them the issue about the AIP (it's very well known) and they should arrange the tow for you.Also please take the time to rate my help (1-5 stars), as it helps me.

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