ECM controlled exhaust brake on 04.5 auto?

[Superdawg]

This is a follow up on another thread titled "ECM controlled exhaust brake on 05 auto". I separated it because mine is a 04.5.

Years ago, the 48RE was rebuilt, Transgo valve body kit and a no name lower stall torque converter. I have been running a Pacbrake PRXB for many years but it only stays in one gear then shuts off. No downshifting and reapplication of the exhaust brake. 175k on truck.

I want to have downshifting with the exhaust brake and a much more simple wire harness.

Can we post the Jacobs and Pacbrake diagrams without violating forum rules?

Sometimes I try to simplify things but end up making it more difficult. In the other thread, a member had suggested following the Jacobs wiring diagram which has one relay covering the solenoid at the vacuum pump.

I did not follow this is because I have a solenoid, pressure switch and power supply for compressor, requiring two relays ( think). And I am electrically challenged. Jacobs diagram has one relay. If what I need can be done with one relay, I need to see it diagrammed out. I ended up purchasing a Pacbrake harness for a 2006 automatic that had two relays because I only know enough about electricity to be dangerous.
Well, I removed the whole Pacbrake controller (rat nest of wires) and wired it up the more simple harness- Pacbrake #C20173 for a 2006 auto 48RE, 03-07 no transmission controller.

Tested it out: Very sluggish, low power. Better power above 40 mph. Exhaust brake seemed like it was at 30% effectiveness, a little better above 40 mph.
DTC: P2769 Torque Converter clutch circuit low.
P0477 Low voltage at the engine brake driver

I removed the left fender liner again and checked the voltage with ignition on at pin 42. .02 volts. Should be 12 volts. I made sure the wires with the pins were properly bedded into the ECM mounted on the side of the engine. Black at pin 42 and white at pin 39. The pin at 42 did seat a little farther down. Now I have 12 volts at ignition on.

Test drive: Same sluggish as before, no change. I cleared the codes and P2769 came back. Maybe the no voltage earlier from pin 42 made the torque converter unhappy? Seems like the trans is in limp mode. Feels like it is stuck in 3rd or 4th gear. Any suggestions to get it out of limp mode? Maybe I will have to try a transmission shop.

I am tempted to rewire it to the Jacobs diagram and add whatever relay I need to to cover the air solenoid for the exhaust brake, the VIAR 350C air compressor (20 amp, 100% duty cycle), and the pressure switch. Also, the Jacobs diagram shows a stalk switch with several wires going to it and I want to use a toggle. Not sure how that would work.

All suggestions welcome.

 

[Ozymandias]

You need to follow strictly to the Jacob's manual for the 04.5 MY.
You need to wire your compressor independently from the EB harness.
Compressor need to run either always with the ignition on or with a separate switch that is driver operated.

The stalk switch is a double switch the operates two circuits at the same time and has a little LED in it that shows activation of the EB.

I recommend to install a little LED within the drivers view to show the state of the TC clutch. I installed mine in the 2 o'clock position at the side of the cigarette lighter socket, in red, so it does not blind me during nighttime driving.

And yes, if your Trans is in limp mode the EB will activate but not the TC clutch, it drops out the moment the throttle goes to zero.
Limp mode goes away at the next start if the problem isn't there anymore that triggered it.
In my case the transducer was bad.

 

[Superdawg]

You know, I have never personally met Ozy but I still wish he lived next door.

On the led for the state of the TC clutch, I read before about a mod to install that. Unless one of these wires in this diagram will facilitate that also.

That's great info and I feel much better now. Between the family, work and incoming rain, I don't think I will get to it for about a week or more. Need to pick up a stalk switch.

Thanks!

 

[Ozymandias]

If I read the diagram correctly then the Switch just provides a ground to Pin B39 to tell the ECM that the EB has been activated by the driver.

Pin B42 then provides a ground to the relay coil once the ECM detects zero throttle input.

The other circuit within the Stalk switch is just for the LED with a resistor to make the LED dim.


Activating the EB with the stalk switch also changes the shift pattern of the transmission, you get later upshifts and TC lock-up logic is more aggressive, means it is more often locked then without the activated EB. Earlier downshifts are also part of it.

 

[Ozymandias]

The P2769 more then likely comes from the leftovers of your Pacbrake harness. It is well known codes for people like me that installed a mystery switch.
The Pac wants to take control over the EB and uses an artifical ground to do so, but the ECM senses this additional ground as a short to ground in the circuit. That's why a Mystery Switch needs an additional resistor put in line to keep that code from popping up.

By the way, this would be the wire you tap into for the TC clutch state LED, this wire provides the ground for the LED. The positive you can take somewhere, usually from the cig lighter socket as it is a switched power.

Additional information: a 33-Ohm 0.5-1A Resistor is all it needs to fool the ECM.

 

[CharlesinGA]

If I read the diagram correctly then the Switch just provides a ground to Pin B39 to tell the ECM that the EB has been activated by the driver.

Pin B42 then provides a ground to the relay coil once the ECM detects zero throttle input.

Ozy is correct the pins on the ECM are looking for grounds (B39) or creating grounds (B42). DO NOT probe them for voltage, there should not be any and you could easily damage the ECM circuits.

In addition to activating the "bosch" relay coil B42, the ECM looks at engine temp. Below 170°F EB is on down to and at idle. Above 170°F ECM shuts off the EB at about 900 rpm decelerating. This is in addition to looking at the PPS for pedal application or not.

Pin 39 connects to the dash switch to tell the computer to operate the EB (via pin 42). The computer is only capable of handling a tiny bit of current so it operates the small "bosch" relays that then take ignition current and pass it to the solenoid air valve that PacBrrake uses to actuate the air cylinder.

This is from the PacBrake instructions.

CAUTION: The white wire goes in to the ECM pin# 39. This is a ground input and under no circumstances should 12 volts positive be applied to this circuit. Damage to the ECM will result.

Charles

 

[Superdawg]

Update.

Rewired the compressor/pressure switch with separate relay and on/off toggle. Works fine.

Rewired EB using Jacobs diagram and new stalk switch 05102082AB.
I can clear out the codes but they keep coming back withing a few seconds of driving:

P0478 High voltage at the engine brake driver
P2769 Torque converter clutch circuit low
Limp mode and codes come back withing a few seconds of driving.

EB is non-operational but as mentioned earlier in the thread, the codes likely prevent EB from turning on.

On my copy of the Jacobs install instructions for ECM troubleshooting under #4, Fault Code 0478 (High voltage engine brake driver-ECM pin B42). The ECM has detected greater than 12 volts at ECM pin B42. Troubleshoot the ECM. Refer to Chrysler service literature.

I can bypass the limp mode by going to nuetral at a stop then quickly dropping the shifter into Low 1 then manually shifting up to drive as speed increases. No other issues noted. Truck operates normally. Fortunately, this is my spare vehicle.

I spoke to a local transmission shop about my issues. They suggested I contact Wranglerfix.com in Florida to maybe repair the ECM. Any other suggestions for ECM repair shops for diagnosing the ECM for proper operation? It is very possible that in my initial wiring attempt, I sent 12 v into maybe B39 on the ECM by messing up the wiring on the relay.

Thanks for the input and keep those suggestions coming.

 

[Ozymandias]

Okay....

First question, is the whole former Pac harness gone??? All the connection taken out, all the cut wires reconnected to factory standard.

 

[Ozymandias]

Because the P2769 has NOTHING to do with what you are doing with the Jacob's wiring - there is NO connection between these two.
This code needs to be fixed first.

 

[Ozymandias]

And NO you don't need to point at the ECM, this is wiring stuff, this will fix it if it is done the proper way.

You have one fault in your factory harness to the TC clutch circuit.

And you have one other fault in the fairly simple Jacob's harness.
If the B42 circuit is perfect then your ECM is likely bad.

And sadly there is a chance, mentioned above, that you fried your ECM by sending 12v down a ground sensing wire.

 

[Superdawg]

I agree with the P2769. That one does not concern me as much as the P0478. This started when I likely wired the relay wrong and could have sent 12 v into the ground.

From the Pacbrake harness, I cut and sealed the wire spliced to the wire at Pin 12 in the ECM. I removed the Pacbrake connector at the factory 3 pin and put the factory cap back on it. I cut and sealed the two Pacbrake wires splicing to wires at the trans connector. It is a lot of wires.

I spoke to an ECM repair place in Florida. They seemed knowlegable and reasonable in their costs to diagnose and repair the ECM if needed.

 

[Superdawg]

The whole Pacbrake harness is gone.

 

[Superdawg]

This weekend I will double check to see if I removed all of the Pacbrake harness.

I will double check (second opinion) I followed the Jacobs diagram with my wiring and the relay.

I wonder if it is possible the P2769 could be collateral damage if the ECM got burned at B42?

 

[Ozymandias]

Probably not but who knows, it's electronics so everything is possible.

You need to clear that TC lockup wire from the ECM down to the transmission, im pretty sure that there is something off with it.

I'm going to check an install manual from Pac to see if I can pinpoint it...

 

[Ozymandias]

These are the today's wiring schematics from Pac.

The thing is - today they do exactly the same wiring as the Jacob's always did.

But I believe not to long ago thy used a Trans Controller not only for the Gen.2 trucks but also for our Gen.3 ones.

If you say you had a bunch of wires I believe you had one of these.

Sad part is I couldn't find any install manuals for these older versions.

 

[Superdawg]

I had the trans controller. I installed it many years ago and still have the instructions. I apologize for not adding that earlier.

When I tried to rewire it the first time a couple weeks ago, I used the first Pacbrake diagram in your latest post with two relays. That is where I think I goofed wiring up the relays and maybe sent 12v to B39. Since then, I wired the compressor independently.

I had not seen your second diagram from Pacbrake before (shown with on/off switch for manual transmission). Yes, very similar to Jacobs.

Is the wire that manages the TC lockup the same one they tap into to add a light on the dash showing TC lockup? I can search for that mod to locate which wire it is on the ECM.

 

[Ozymandias]

For the trans controller (installed one in my buddies '98) you have to cut the TC lockup wire somewhere. You need to find that and reestablish that connection. Right now your ECM senses a short to ground from that wire.
If you still have that install manual in paper form, please do a photography of the wiring diagram and upload it here.

 

[Superdawg]

How does it feel to be correct, Ozy? I reread the instructions at number six several times. After what you said again about splicing the wire, I read it again. Apparently I did cut that wire at the transmission connector according to the install instructions. When I removed the harness, I just cut and capped the wires without reconnecting the TC wire. Now I understand. I can be thick headed at times. With any luck, it will take care of maybe one or both of my trouble codes. I will dig into it on Saturday and let you know.

 

[Ozymandias]

Well, let's hope for the best and expect the worst then. You can do it.

 

[Superdawg]

Update:
I reconnected the wire at the transmission connector and both codes went away. No codes showing. Progress.

EB not turning on. Going through electrical troubleshooting list per Jacobs install instructions now.