2007 Prius - Codes C1515, C1203, C1345 & C1354

So I just picked up my first Prius from a neighbor who had taken the car to an independent shop for brake troubles. The shop told her that the car needed a new brake accumulator. She paid them over $2,000 to put one in, the brakes still did not function as expected. The shop then said the car needed a new skid control ECU to the tune of another $1,700. She did not have them install a new skid control ECU and decided to cut her losses and sell the car as is.

After buying the car, I picked it up from the shop. While there, I talked to the mechanic who had worked on the car. I asked him what codes were present, and he just said whatever ones say it needs a new skid control ECU... not very helpful or confidence inspiring. The car has 150K, a two year old hybrid battery and is in great shape with the exception of the brake and steering issues, so I'd like to bring it back to life.

I bought a mini-VCI off eBay and installed techstream to pull the codes. The dash is lit up like Christmas, but there were only 4 codes:

C1515 - Torque Sensor Zero Point Adjustment Undone (steering related I assume as the car's power steering is not working at all, PO said the steering was fine when it went into the shop)

C1203 - Engine Control System Communication Circuit
C1345 - Not Learning Linear Valve Offset
C1354 - Increasing Pressure Solenoid (RR)

From reading up on C1515, it looks like this can be fixed by resetting the zero of the torque sensor. The other three are definitely brake related.

Outside of the drive home from the shop, I've only driven the car around the neighborhood to test. The brakes are definitely wonky. The only brakes that seem to be working are the driver's side brakes. The car pulls left, and after multiple stops, the drivers front and rear brakes are warm to the touch, but the passenger side brakes are completely cold.

I do all my own work on my cars and have done pretty much everything from oil changes to full engine replacements and pretty much everything in between, but this is my first time digging into a Prius. From what I gather, the brake pedal is actually just connected to a stroke simulator and the ECU controls the pressure applied to each caliper. I've read the brake bleeding procedure in the manual and watched a few videos of the process using techstream. My thought is to first re-bleed the brake system using techstream before I start swapping parts. Am I headed down the right path or do the codes indicate that I need a new skid control ECU like the shop said? Any help is appreciated.

 

UPDATE: I was able to clear the C1203 and the C1515 codes. The only codes remaining are:

C1345 - Not Learning Linear Valve Offset
C1354 - Increasing Pressure Solenoid (RR)

I've replaced the skid control ECU with a known good unit and the codes still persist. I spoke with the shop that installed the accumulator. They have installed three different accumulators in the car, one was a new aftermarket, two were new Toyota units. If the ECU is good and the accumulator is good, what are my next steps? Only possibilities at this point are wiring? Or is there something else to check. Also, the 12V battery is new as of November 2020 and is fully charged, so its not that.

 

Thanks, I've ordered a set of back probe adapters for my multimeter from Amazon and will test once they arrive. I found a copy of the wiring diagram for the car and will start with the ECU side (S10 connector, pins 9 SLARR- and 19 SLARR+). Looks to be pins 11 & 12 on the actuator side of things. Purple and pink wires. There was not any INF detail available on Techstream (the snowflake was grayed out). I'm using an earlier version, so may need to upgrade.

 

The back probe kit arrived last night, so I was able to test this morning. Verified that there is no break in the wiring harness. Both the positive and negative SLARR wires were under 1Ω from the connector at the ECU to the connector at the actuator. No short to ground for either wire either (open connection).

When you say that the proper Solenoid resistance should be 3.5-4.3 Ω (couldn't find this number in the manual to verify I was checking the correct way), you are talking about the resistance between the SLARR positive and negative wires themselves? If so, I get an open reading when testing at both the ECU connector and the actuator connector? Maybe I'm not doing it right? For this test, the ECU should be unplugged but the car in On-Ready?

Thanks again for your help!

 

Also, upgraded my Techstream to version 15.00.026 and still am not seeing any INF (snowflake) data available? I did pull the data list and the SLARR circuit is showing 0.00 while the other circuits are showing 0.49 to 0.52 when I press the brake.

 

I think we solved it, thank you for your help!!! I believe the SLARR+ wire has a break somewhere within the harness. I went back through all the tests with the multimeter and was able to get a reading of 4.1 Ω on the SLARR circuit at the actuator, but not the ECU. All other SLA circuits had readings at both the actuator and ECU, which again pointed to a wiring issue. I re-tested both SLARR wires for continuity and both were initially reading less than 1 ohm. I left the multimeter connected for a much longer time on each wire and noticed that the SLARR+ (purple wire) would fluctuate wildly from time to time and then go back to less than one ohm. The SLARR- (pink wire) never fluctuated at all, leading me to believe there was a break somewhere inside the harness that would intermittently disconnect. I decided to test the car with Techstream using the back probes on the ECU and Actuator as a jumper cable for the SLARR+ wire and confirmed that the C1354 code was gone!

Now the question is, do I order an entire harness and tear the car apart, or just re-run the single offending wire with some posi-taps...

Thank you again for your help!

 

That you for all you help, repair is done. Did some more testing once I pulled the plug off the actuator. Ended up.that one of the female connections in the plug was not connecting. When I was back a proving it would occasionally create a connection. After bending the female connector back to normal, the connection is perfect and the codes are gone.