2005 Rainier (SUV) 5.3L E40 VCM- no fan PWM from AC pressure

[V8 Supra Builder]

I have sent this up the chain through support, and Bill suggested I post here since they can't find anything in the software:

Setup:
2005 Rainier, 5.3L LH6, stock engine other than DoD removed.
Cooling system mods- Mercedes PWM cooling fan (selected for fit), it has an internal controller, so big wires power and ground then a small wire for PWM input. Tested with a generic PWM generator and it needs reversed duty cycles, i.e. 10% PWM= 90% duty and 90% PWM= 10% duty. It is wired via the old electro-mechanical fan connector- I re-routed the proper wire from the VCM to the new fan, and then spliced it to the Mercedes pigtail.

I have the tuning credit for this VCM and have used it to adapt the fan. Using the inverted settings, the fan works great based upon coolant temp- usually need only about 30% duty cycle on a hot day at idle.

Problem:
The fan does not come on at all based upon AC pressure.

When in VCM scanner, I found I can see the AC pressure and volts. I can also manually activate the fan by setting a duty cycle within range. The sensor is working properly, and its output is making it to the VCM.

Question 1:
I read some helpful posts from blindsquirrel in this thread that dealt with a similar issue on an E38. Is it possible the truck VCM has some difference in internal circuitry vs the Corvette (it doesn't seem like this would be significant, see OS data below where Corvette used all 3 numbers, but maybe it's a hardware issue)?

Question 2:
Would a segment swap be in order here as was done in that thread? If in fact there is an internal difference between the Corvette and Buick VCM, that may be a way to overcome the problem.

Not a solution:
I did try switching from PWM-Electric (Corvette) to PWM-EV (Buick) and it did not turn on the fan. It also did not allow me to manually turn it on via scanner.

Additional data:
I looked up the AC pressure sensors on a parts site, and they are different part numbers, but both are 5V sensors, so the output is the same. I also checked some OS data:
My VCM is using OS 12598983.
I opened a stock 2005 Rainier 5.3 tune from the repository and it had 12596660.
I opened one from a 2005 Corvette and it used 12605740.

From what I've read on another forum, all three of these were used on the 2005 Corvette. The member there reports the 8983 and 5740 use the same calibration but different OS, while the 6660 uses a different calibration.


I have a GM Service Information DVD and looked up the AC sensor data on both vehicles. Here?s what I found:
Both sensors are 3-wire units. All pins have the same functions and go to the same PCM terminals (the 5.3L LH6 Buick; the inline engine is different but that is not a factor for me):

1.Ground

2.5V supply
3.Signal

In the system description, here is what it says about the pressure sensors for both. It looks like both use the same 5V reference setup. I have marked some differences in red, and my comments are in red italics:
--------------------------------------------------------------------------------


2005 Buick Rainier AC Pressure Switch Operation:
A/C Refrigerant Pressure Sensor
The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5-volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts. The powertrain control module (PCM) converts the voltage signal to a pressure value (does this happen in C6? No information.).

The A/C refrigerant pressure sensor protects the A/C system from operating when an excessively high pressure condition exists. The PCM disables the compressor clutch if the A/C pressure is more than 2413 kPa (350 psi) (2850 for C6). The clutch will be enabled after the pressure decreases to less than 1578 kPa (229 psi) (2100 for C6). This sensor does not have a low-pressure protection setting as the C6 one does.
There is no mention of the PCM sending an invalid message via class 2 serial as there is in the C6.
2005 Corvette AC Pressure Switch Operation:
A/C Refrigerant Pressure Sensor
The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5-volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts.
The A/C refrigerant pressure sensor prevents the A/C system from operating when an excessively high or low pressure condition exists. The ECM disables the compressor clutch under the following conditions:

• A/C pressure is more than 2850 kPa (413 psi). The clutch will be enabled after the pressure decreases to less than 2100 kPa (254 psi).
• A/C pressure is less than 204 kPa (30 psi). The clutch will be enabled after the pressure increases to more than 220 kPa (32 psi).

If the ECM detects a failure in the A/C refrigerant pressure sensor or circuit, the class 2 message sent to the HVAC control module will be invalid. The HVAC control module will display A/C OFF on the module as long as the condition is present.
---------------------------------------------------------------------------------------------------------------------

I'll attach my most recent hpt file for reference.
Rainier_122120_C6 fan mod raised ECT and AC press numbers.hpt

[V8 Supra Builder]

Apparently an unsolvable problem. I'm working on adapting an Arduino to control the fan based upon temperature and pressure inputs. It's a lot of work and may not work at all. If it does, I'll update here.

[cadillactech]

Attached at the 2005 Rainer cooling fan schematic and the 2005 Corvette cooling fan schematic.

Rainer Cooling Schematic.jpg

Corvette Cooling.jpg

The pin outs are quite different.

Now I am trying to understand what you have. Vehicle is a 2005 Rainer with stock LH6 but you removed the electro/viscous fan for a Mercedes PMW one? Where does the 2005 C6 cooling fan system come into play?

That being said, these both are E40 ECMs but different internally for sure in stock form and different part numbers. In order to segment swap, the OS much match exactly.

The factory setup on the electro/viscous fans is unique compared to the PMW fans. Which wire are you using for the fan control from the factory wiring?

[V8 Supra Builder]

Attached at the 2005 Rainer cooling fan schematic and the 2005 Corvette cooling fan schematic.

The pin outs are quite different.

Now I am trying to understand what you have. Vehicle is a 2005 Rainer with stock LH6 but you removed the electro/viscous fan for a Mercedes PMW one? Where does the 2005 C6 cooling fan system come into play?

That being said, these both are E40 ECMs but different internally for sure in stock form and different part numbers. In order to segment swap, the OS much match exactly.

The factory setup on the electro/viscous fans is unique compared to the PMW fans. Which wire are you using for the fan control from the factory wiring?

Thanks for the reply. I have attached an annotated combination of your pics for comparison. Key points:
The C6 uses a fan module that supplies power, ground, and accepts the PWM signal from C1-36. The VCM does not control the power or ground, as these are high-amp large gauge wires.
On my truck, the power & ground are supplied via a mega fuse and similar heavy gauge wiring. Pin C1-36 went to a relay in the Buick. It was re-routed to the PWM input on the MB fan. This is a key wiring point.

The other wires shown on the C6 VCM are the same on the Buick- C2-55 ECT signal, and C1-1 & 2 serial data.

The added complexity in the upper right (HUD and info center) appear to not affect fan operation, just report data on it.

Not shown but worth noting are the 3x AC sensor wires. They are identical in function and location for both vehicles. While the C6 uses higher-pressure cutoffs, they are both 0-5V sensors and the difference in voltage will not be that significant. Looking at the cut-on KPA in the OEM C6 HPT file, the fan should come on sooner vs later as it kicks in at a relatively low 725 KPA.

I'll also attach a spreadsheet I wrote that contains the pinouts for the Buick, C6, and GTO from 2005.

Finally, I'll attach a combined screenshot of the Buick and C6 HPT stock file fan settings.

What is telling to me here is that the VCM can control the fan perfectly based upon ECT. It also reads the AC pressure sensor, leading me to believe it is not an external communication issue. The clutch is slipping here between the pressure signal being received and output via PWM.

EDIT
I left off some info on the combined pic. The updated one is attached. I've also attached a PDF of my design page for the conversion.
Rainer vs C6 Cooling Schematic text.jpg

2005 E40 Pinouts Rainier-C6-GTO.xlsx

2005_Rainier_vs2005_Corvette_fan_settings.jpg

E-fan_conversion_MB.pdf

[cadillactech]

I downloaded a stock 2005 C6 file from the repository and found that your Desired fan vs AC pressure setting do not look like what you have in your current calibration file.

Have you tried copying those over?

[V8 Supra Builder]

I downloaded a stock 2005 C6 file from the repository and found that your Desired fan vs AC pressure setting do not look like what you have in your current calibration file.

Have you tried copying those over?

They look different because they are reversed. On my fan, 90% duty cycle = 10% fan speed, while on the C6, 90% duty cycle= 100% fan speed.

I have tried various duty cycle settings there and none have caused the fan to come on.

[cadillactech]

They look different because they are reversed. On my fan, 90% duty cycle = 10% fan speed, while on the C6, 90% duty cycle= 100% fan speed.

I have tried various duty cycle settings there and none have caused the fan to come on.

Got it. I read that but did not put it into context for your set up.

Kind of stumped right now, will try to spend some time looking through the cal again later today and see if I see anything.

[V8 Supra Builder]

I've been working on a solution involving a microcontroller (Arduino) and as of today have tested it on the truck using a potentiometer to simulate the output from the sensors. Here is a link to my single post on LS1tech.com where I discuss it and have files attached.

I have not hardwired it in as yet, but confidence is high that it will solve the problem. I'll try to post back with an update either way.

[cadillactech]

I will have to sit down tonight and read that whole thread, lots of great info in there! Thanks for sharing, hopefully this is the solution. Kind of a bummer we can't get the factory ECM to control it!

[smokeshow]

I've been working on a solution involving a microcontroller (Arduino) and as of today have tested it on the truck using a potentiometer to simulate the output from the sensors. Here is a link to my single post on LS1tech.com where I discuss it and have files attached.

I have not hardwired it in as yet, but confidence is high that it will solve the problem. I'll try to post back with an update either way.

I've been running mine this way for a couple years. Standalone controls on a Cortex M7 based auxiliary controller. Don't regret it at all, although later I found a number of devices on the market very similar to the one I wasted too much time on and developed from scratch lol.