Toyota's luxury arm, Lexus, makes some of the most reliable luxury cars on the market. Like the mother company, it is what the brand is known for. Granted, there have been a few hiccups on Toyota's behalf lately, but overall, the Japanese company retains a near-spotless reputation for reliability. That said, a member of the Club Lexus forum shared an interesting issue and it seems the cause for it is still unknown. The car in question is a 2006 Lexus RX400h and here's what the owner is saying:
“Full throttle, coolant temp warning for like one second. Loud bang pop under the hood, left side. I though driveshaft, but no. Engine running, no power. Coast to shoulder. No movement, but engine ran WITH COOLING FANS fully running. Could not shut down cooling fans even with the key off. I killed the battery. Towed it home. Car jump started to try and get off the trailer. Fans on, no power, no start. Now, no ready and plenty of dash lights. Checked hybrid battery fuse block. No corrosion or water in the hybrid battery. Engine temp sensor? Inverter blown? A/C issue? Please help.”
Certain problems look serious due to the symptoms. In this case, the car was out of commission. Luckily, the mechanical was prepared with knowledge, skill, and the right equipment to diagnose the problem. Some guesswork from other members, going off the owner's described problem, as well as sharing of car schematics, also helped out in determining the cause of the issue. If you encounter similar symptoms to what the owner described above, here are some pointers that may put you on the right track:
LeX2K says: “Broken axle? Are you sure not? Inverter under the hood exploded? Have a peek under the car see if the axles are in one piece or any other damage.”
Tammap says: “Are you mechanically inclined and handy at DIY?
Is your scanner bidirectional and can read subcodes (info)?
Check your auxiliary battery voltage ≥ 12.4 volts.
I suspect you might have issues with your DC/DC converter inverter assembly's cooling system, possibly an auxiliary water pump or hoses. Take a look at the reservoir tank, if it's empty then you might have busted coolant hoses or the auxiliary water pump is cr*pped out.”
The problem ended up being something relatively minor
The issue is resolved and the owner shared an update post-fixing it. What, initially, looked like a potentially catastrophic failure that would offset the value of the hybrid Lexus SUV, ended up being a blown fuse. Here is the update from the owner:
“Update igc2 fuse replaced, rear hatch works now, replaced inverter, car starts, power to HVB relay block, relay functioning. Low on engine coolant, but not reservoir bottle. Hmm, a gallon low. No visible leaks. Still have to scan car. Service hybrid and coolant light were on dash. I did not clear codes yet. Its late. Baffled as to low coolant level. So my hypothesis, coolant level low triggered issue? Have to look up IGC2 fuse circuit unless someone knows what it controls. Motor runs fine, will do exhaust test for antifreeze later, and rad pressure test. Still have to run another scan.”
The Lexys RX400h owner added another thing worth looking out for:
"Brand new radiator 1year ago, from Japan. I think the hose from the reservoir to the radiator clogged up, giving illusion of a full radiator. Will put dye in the radiator. I had a small hairline crack in radiator and bad radiator cap when I bought it 3 years ago. Hope no hairline crack in head, sucking coolant. I tested radiator pressure and exhaust gases when I installed new radiator and dyed anti no leaks all were good back then.???? Why did IGC2 fuse blow? Hmm...”
Here are some of the codes the owner got when using a scan to diagnose the issue:
From my research, it seems this isn't a common problem of the Lexus RX400h.
No database documents this as a common issue of the 2006 Lexus RX400h. While some forum members recommend to look out for the battery and invertor as these two are main components of the hybrid powertrain, and can be pricey to replace if they go bad.
According to Repair Pal, there was one documented service recall for the 2006 Lexus RX400h. It concerns the deteriorating brake performance, due to a brake line leak. This issue affected a total of 13 Lexus models from those years.
The owner seems to be getting somewhere with this issue and replacing the IGC2 fuse and a few other parts seems to have improved the situation. This goes to show that even models as reliable as Toyota and Lexus cars from the 2000s may, eventually, suffer more serious problems. Even new Toyota models can suffer some strange issues. I recently reported on a 2020 Toyota Corolla that had a slight issue, due to a small mechanical part failing.
I am following the thread as the owner continues to dissect the issue and replace parts. Uncommon issues are trickier to deal with as there is far less information on them and how to fix them. Despite that, the Lexus RX hybrid continues to be a popular choice and a generally trouble-free proposition on the SUV market.
Dimitar Angelov's automotive interests made him an expert in a wide variety of vehicles. Japanese brands like Toyota are closest to his heart, although performance cars in general are his favorite segment, which is why he is constantly on the lookout for the best deals on the market. Dimitar Angelov's car passion and knack for the written word led him to complete a Master of Arts in Media and Communications, and classic car restoration. Dim is happy to get behind the wheel of any car and share his impressions. You can follow Dimitar on X, Linked-in, Instagram, and Facebook.
Image source: 2006 Lexus RX