DBW Cruise Issues
Thread Starter
Teching In
Joined: Feb 2014
Posts: 29
Likes: 1
From: Independence, OR
DBW Cruise Issues After a four year build I've got my project on the road, but can't seem to find my cruise issue.
Backgroud:
2005 LM7 with a 4L60e, original TAC and Accel pedal and BP harness. Vats and base program done by Brendan a lt1swap.com.
Operation is solid and other than a Bank 1 O2 Sensor code setting, no problems but the cruise.
On the first test drive the cruise engaged and worked once. Since then no luck.
Have tested inputs from the cruise lever to the TAC on pins 4, 14, and hooked 6 direct to ground. Still no go.
Checked the TCC signal to the ECM on pin 33, and that checks out good too.
I don't have a full featured scantool to check the ECM for cruise codes.
Any thoughts at this point would be appreciated. Thanks for all the info shared here.
Backgroud:
2005 LM7 with a 4L60e, original TAC and Accel pedal and BP harness. Vats and base program done by Brendan a lt1swap.com.
Operation is solid and other than a Bank 1 O2 Sensor code setting, no problems but the cruise.
On the first test drive the cruise engaged and worked once. Since then no luck.
Have tested inputs from the cruise lever to the TAC on pins 4, 14, and hooked 6 direct to ground. Still no go.
Checked the TCC signal to the ECM on pin 33, and that checks out good too.
I don't have a full featured scantool to check the ECM for cruise codes.
Any thoughts at this point would be appreciated. Thanks for all the info shared here.
Thread Starter
Teching In
Joined: Feb 2014
Posts: 29
Likes: 1
From: Independence, OR
I'm not using the 4 prong switch due to the master cylinder being under-floor instead of under dash. My brake switch is the toe board mounted one used in the advanced series trucks, then run to relays to handle the need for both open and closed circuits
Thanks
Thanks
Thread Starter
Teching In
Joined: Feb 2014
Posts: 29
Likes: 1
From: Independence, OR
The cruise switch is a 250-3020 Rostra switch with a Rostra 250-2891 N/C to N/O adapter. Yes I have LED brake lights.
I had the brake lights wired with a relay to deal with the lack of resistance. Then bypassed the relay with a direct to ground connection for the TAC module on Pin 6(for simpler diagnostics).
I also have the TCC wired using a relay with correct power feed to the ECM on Pin 33, (purple wire).
The only possibilities I can think of are a cruise code (inhibiting cruise operation), or electrical damage to the TAC or ECM (doubtful, but I'm running out of ideas ...).
I had the brake lights wired with a relay to deal with the lack of resistance. Then bypassed the relay with a direct to ground connection for the TAC module on Pin 6(for simpler diagnostics).
I also have the TCC wired using a relay with correct power feed to the ECM on Pin 33, (purple wire).
The only possibilities I can think of are a cruise code (inhibiting cruise operation), or electrical damage to the TAC or ECM (doubtful, but I'm running out of ideas ...).
Thread Starter
Teching In
Joined: Feb 2014
Posts: 29
Likes: 1
From: Independence, OR
Could you clarify this a little?
My understanding was that the TAC/ECM is looking for resistance from the lamps on the circuit. So having 12v on the circuit instead of the ground makes more sense than a direct ground. Don't I need some resistance too (resistor, lamp)? I've seen the posts on this but was trying to simplify the situation until, I got a better result....
Sorry the guys who sold me the adapter, gave me the "just ground the light blue wire" suggestion. In fairness I probably misunderstood....
Thanks again for helping!
My understanding was that the TAC/ECM is looking for resistance from the lamps on the circuit. So having 12v on the circuit instead of the ground makes more sense than a direct ground. Don't I need some resistance too (resistor, lamp)? I've seen the posts on this but was trying to simplify the situation until, I got a better result....
Sorry the guys who sold me the adapter, gave me the "just ground the light blue wire" suggestion. In fairness I probably misunderstood....
Thanks again for helping!
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The TAC "sees" a ground through the brake light circuit, so yes you do need some resistance in it, hence the reason I asked about the LEDs. Hook that light blue wire from the TAC to the cold side of the brake light switch, so that it sends 12v to the TAC at the same time it sends 12v to the brake light bulbs. For resistance, you can just wire up a relay to the same place so that the relay is energized when the brakes are applied. You are just using the coil of the relay for resistance so no need to hook anything else up to it. You could also use an 1157 bulb as a test, that will work too.
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Verdad Gallardo Also just an FYI, both brake circuits need to be hooked up, the normally closed one to the PCM and the normally open one to the TAC. They also both have to see a brake input once at every ignition cycle before the cruise will set.
Thread Starter
Teching In
Joined: Feb 2014
Posts: 29
Likes: 1
From: Independence, OR
Thanks for your help it works now.
Got on it with a clear head today and realized I had wired my relay to handle both the TCC signal and the Cruise disconnect. I believe the only issue was the lack of resistance in the taillight circuit with LEDs.
Today I wired a single 1141 bulb into the circuit and it worked like a charm.
I probably will use the original relay setup and just add a resistor. Second choice is a relay for the resistance....
Thanks again for the help!
Got on it with a clear head today and realized I had wired my relay to handle both the TCC signal and the Cruise disconnect. I believe the only issue was the lack of resistance in the taillight circuit with LEDs.
Today I wired a single 1141 bulb into the circuit and it worked like a charm.
I probably will use the original relay setup and just add a resistor. Second choice is a relay for the resistance....
Thanks again for the help!
Last edited by Tom2T; Mar 27, 2019 at 12:47 PM. Reason: spelling