UPDATE:
It is fixed! Replacing the dc to dc converter under the battery did fix it. Initially I had replaced the ecu (I thought it was the dc converter). The wire diagram picture is slightly confusing the 3 inputs on the diagram make it look like the ecu. I hope this helps someone avoid my mistake.


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This one has me stumped.

- Parts replaced so far with no change:

1.-Battery (lexus warranty)
2.-Alternator (autozone)
3.-Steering ecu P/N 89650-50140 ( ebay used)

I only get the error on cold nights once the car is cooled off.

On cold mornings I get this fault along with no power steering assist. After the car has run for 30 seconds in park, I can restart the car and the steering operates normally with no messages on the dash. The car will operate normally for the rest of the day. One exception to this is if I drive the car a short distance shut it off and let it cool off for a couple hours. Then I will get the fault again. Once the car parks overnight the same error repeats in the morning. .

On a warmer day If I open my garage door slightly over night to make our garage a little cooler the error will come up. If I keep the car warm over night there are no issues with it in the morning.

Some cold mornings the fault will come on for 30 seconds and go off on its own if I leave it in park. If I shift into reverse with the fault present it will not go away until I restart.


I've been dealing with this fault for over 6 months. I've gotten the fault in excess of 30 times. I have techstream installed on my laptop, here is the freeze frame data. All the data I have gathered so far indicates the steering module ( computer ) is bad. However I installed another computer P/N 89650-50140 from a salvaged car. The used computer gives the exact same faults. The voltage on the freeze frame data has always been within the limits for normal operation (on both the original computer and the used one I bought)

When the outside air temp is over 100f I do not get the fault. I do not get the fault for months in the summer. This is the only good thing about Phoenix summers.

I had this fault before I replaced the battery and the alternator. They were replaced about 3 months ago. I didn't replace them specifically for the steering fault. The battery failed and the alternator failed a week later.

Did I replace the correct steering module? Does anyone have a wire diagram for this specific fault? Any help is appreciated. Maybe wrap the car in a blanket overnight

Thanks, Mike

 

I bought the same mod for a steering issue i had but never used it. My issue cleared up after a month. Did you recalibrate the steering after you replaced the mod? Not sure how its posted in here somewhere and you use techstream.

 

You may have a defective starting battery. When a battery has a defective cell, the voltage is lower, but often is still able to supply enough current to start the car. The car's standby load lowers the battery's voltage when the engine is not running. When the car's engine is running the charging system raises the voltage by raising the State Of Charge. The car warns when the battery's SOC is too low to reliably operate the car's electrical power steering. Have your battery tested by reputable battery dealer.

 

Thank you for the replies.

The battery was replaced under warranty by lexus a few months ago. I have put a load meter on it in the morning, it checks good. I don't recall the exact cca but they were within the battery specs.. I had the same steering fault with the previous battery too. With the previous alternator I also had the same steering fault

I did re-calibrate the replacement steering module using techstream after I installed it. Technically I waited a month. It had the same c1552 fault before and after the calibration.

There have never been any other steering faults only the c1552. At least in the history that I see using techstream.

 

Well, I believe the car uses battery SOC to determine when to warn of compromised steering. I think it would be a good idea to measure the SOC to see if that provides any insight.

Low SOC could be an indication of a defective battery, charging system problem, battery cable problem or something like that. We don’t see many reports of defective alternators in this forum.

You can find a Temperature Compensated Battery SOC Table at this link: https://offgridham.com/2016/08/storage-batteries/

 

I agree the problem could very well be the battery.

My alternator definitely died last year. My car had a new battery in it (the one in it now). 15 miles from home I lost power brakes, power steering, air conditioning, and the nav display in the car shut off. I even lost turn signals once I got close to home. I was lucky to make it home without a tow. I charged the battery up and measured voltage with the car running. Alternator wasn't putting out anything. That trek home could have damaged the battery too.

Here is a freeze frame screen shot from yesterday when it faulted. The voltage is 13.xx. I ordered an oscilloscope yesterday. While techstream is nice it's only as accurate as the faulty sensor it reads
I'll post back once I get some data of my own.

 

Voltage drops to 9.38v during start.

In the morning the battery state of charge is definitely an issue. I'm fairly sure over the course of a night the brake booster motor is draining the battery. I've started to notice over the past week the brake motor is running very often in the garage and while driving. My only guess is cold weather is causing the brake motor to run more. The brake actuator isn't throwing any codes yet but it is making abnormal noises. It looks like I'll be changing the brake actuator next either way.

 

I think you are measuring the alternator voltage instead of the battery voltage. If the battery was fully charged, the battery temperature was 120 deg F, and the State Of Charge was 100%, the voltage would be 12.66 V, the highest the voltage can be. It's chemestry and physics and it can't be higher than that. If the battery was connected to the car overnight the SOC could not be 100%, even if the battery is brand new and the temperature is likely much lower than 120 deg. You want to know what the battery voltage is before you start the car and you need the battery's core temperature to determine its SOC.

 

Jmcraney thank you for looking at the data so closely. I should have explained more. The program that records the oscilloscope data to my laptop displays a data point every second or so. With the engine cold it took 2 starts to capture the low voltage reading. The engine was running a few seconds before the 12.7 readings, the alternator charged the battery for a few seconds. You can actually see in the graph the 2 starts. Battery voltage before the first start was 12.5v. The other day I measured a low sitting battery voltage of 12.46. On a warm night in the morning the battery is at 12.6X.

 

I do understand the battery needs to be disconnected for a few hours to get an accurate soc reading.

The fact that a temperature difference of only 20f (70f vs 50f) causes the battery to read 12.6 vs 12.46 is what perplexes me. I'm convinced the car is putting an abnormal load on the battery on a cool night. The only clue right now is the brake motor running multiple times.

 

This what I could find about the DTC

 

Well, the 12.6V vs 12.46V is within range of a good battery - about 75% SOC, but what you describe seems abnormal. Using the voltage method to determine SOC can be misleading because you are measuring the voltage of 8 cells in series. One cell that is defective in series with 7 cells that are young chemically, can look like 8 cells that are chemically old. The way to resolve this is to measure the specific gravity / SOC of each cell using a battery hydrometer. The hydrometer method is the gold standard of battery evaluation. If you measure the specific gravity of each cell and one cell is much different than the others then that is reason for concern. Inexpensive battery hydrometers are available at most auto parts stores.

When you use the hydrometer, keep in mind that the liquid in the battery is acid and a drop on a painted surface will damage the paint. And, be sure to wear eye protection as batteries emit explosive gases and are subject to explosion.

 

Does anyone know where the power steering ecu is located? I found a picture online of it mounted at the bottom of the glove box in 2010 models. Mine is a 2007 it must be located somewhere else. I'm not sure if this is a valid p/n for my car but this is the p/n for some models 89181-50090

I left my charger hooked up to the car battery overnight even with a fully charged battery the same power steering fault is displayed (garage door was opened during the night to make the car cold). The battery was floating around 13.45 volts. It did about 600cca on my load tester. I am familiar with hydrometers. I probably have one laying around somewhere. For me the oscilloscope confirmed the battery is good albeit a little low on charge on a cool morning (without a charger hooked up). Just for kicks I'll put it on a charger tonight and let it sit for 2 hours and then take a voltage reading.

I'd like to check the pins / connectors on the steering ecu and possibly order another one. To clarify I need the location of the power steering ecu, not the power steering converter assembly.

Thanks, Mike

 

Here you go.

 

I'm confused. In the pdf it is labeled a power steering ecu. In the picture ( wire diagram) posted a few posts above it is called a power steering converter assembly. In any case I've replaced that one under the hood on the right side of the engine compartment. There is another one on all base 460's right? According the the wire diagram above there is a power steering converter assembly and a power steering ecu.