Ambrose's shock decision stunned the V8 Supercars community and fans when announced last week. He sits 12th in the Championship after one points round at the Clipsal 500 in Adelaide.
Here, he talks more in depth about how he has to step backwards to move forwards.
The question on everyone's lips is why?
"Well, it's a combination of factors that got to the point where I decided - and it was fairly obvious to me from driving the car for DR Team Penske that I've come down here to be the lead driver of a single car team and I can't deliver what's expected of me as a lead driver in the circumstances that are around me.
"And there's a number of factors - testing restrictions, tyre restrictions, the weekend formats are pretty condensed - and so I'm learning on the fly, I'm learning in race conditions. And then you throw in the fact that these cars are very difficult to pass, so qualifying really dominates the race results.
"The feel I'm getting from the car is not what it used to be and so I came to the conclusion, and a fairly solid one, to lead the team forward, you need to keep improving the engineering of the car you need to ultimately deliver race results. And the expectation of me to deliver that, when DJR Team Penske now, is not synced together."
The anomaly in all that is, in order for you to get up to speed, you need miles - but you're not in the car. How are we going to solve this?
"Ultimately it's a result of the restrictions on the series. I don't want to get out of the car; I love racing cars, that's what I do for a living. But the team can't wait for a driver to get reacclimatised - you can't lose a year in this game. We've got Roger Penske to come into our series, we want to do as well as we can for him, we want to get him up there as quick as we can. So there's this misalignment between a driver like myself to come back into the series, the way we tried to do it catching up in time, without wasting races. Races cost money, serious money, and as a minimum I'll be doing co-driver races for them and co-driver testing on the race weekends and we'll just see how it goes."
How did you tell Roger [Penske] and how did it go?
"It's not a phone call you want to make, it wasn't an easy phone call to make, but when I outlined how I felt and what I thought was going to be the best, he accepted.
"And he's been unbelievable to work with, the whole company has been incredible, because there's so much disruption when you make a decision like this. This is not something you take lightly - there's sponsor commitments, there's people who have got your name out there on race suits and car designs, and sponsors you've helped bring to the team - there's a lot attached to a lead driver in this series, like any series.
"I just appreciate how they've handled it and how they've respected my opinion and what I said, and we've worked through it together."
Was there a period of doubt in your own mind about your own ability?
"Well - yeah. I mean, I'm 38 now, I've raced all around the world and I've done a lot of races, there comes a time when you come back and you've got to relearn again. It's like, well, can I relearn this, can I do this again? That's certainly, that's not a factor in the decision, but certainly you'd be a fool if you didn't consider where you're at and what you're all about and whether you can step up and take it to them."
Pretty wild rumours in recent days - you're not venturing back to NASCAR are you?
"There's no NASCAR on the horizon, there was no trip to Alice Springs and visiting Uluru - you know, this has just been a difficult decision to make but I think in the best interests of the team, allow me to reset my clock, just to slow it down some.
"We'll jump in this car when the time's appropriate and time will tell when that should be, depending on how Scott goes in the car and how it's all going for the team. But certainly for me personally it just slows it down in 2015 and we can reassess as we go."
What's the role you're going to do this weekend?
"We'll work that out as we go this weekend, but my first goal of the weekend is to face the music to the fans. Talk to the fans and see them - good, bad, ugly, whatever comes my way, I'm going to have to deal with them."
Is your heart still in it - you've not had a change of heart?
"Yeah - there's no doubt that I love racing, I love racing cars and I love being in Australia. Racing V8 Supercars was a ton of fun.
"What wasn't fun was having this doubt that I could lead the team forward like I was expected to. And that was the challenge for me personally and that's been the big issue. Even if I was running 20th - but I could feel the car like I need to, to move this team forward, we wouldn't be having the conversation, but it's been tricky for me to find that.
"And it's just a matter of circumstance around me personally, the experiences I've had to get here are different and I don't have time to wait. We don't have a year to throw away here just to get back into the series - you guarantee after six or seven races if we haven't turned around and the pressure's turning on about being replaced anyway. So let's just get in front of it, get aggressive with it and try and keep the team moving forward.
"Time will tell us exactly what we need to do and it'll make it obvious, the next step. Right now, Scott's in the car for Symmons Plains - we'll have a really hard look at ourselves after Symmons Plains and see how our first three races have gone and we'll start making calls from there. So everything's' on the table here, we're not hiding anything from anybody. We just don't know how it's going to play out."