Help with Cruise Control Diagnosis - JeepForum.com
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post #1 of 33 Old 05-27-2021, 06:25 PM Thread Starter
afnan
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Help with Cruise Control Diagnosis

Hi,

I have been trying to figure out why my cruise control would not turn on. The car has no pending or stored codes. When I failed to resolved it I sent to dealer who said they don't know for sure but suspect the switch. I have tested the switch and it is within the resistance specs. Furthremore, I can see the status of buttons pressed in all modules.

I was thinking this could also perhaps be because of the brake signal problem. The dealer gave me the wiring diagram (attached). I have found by using the scanner that Brake Switch status DOES NOT change in TIPM and WCM. In all other modules it worked fine. Now I am trying to find out why. The switch is new.

1. It would be great if someone could point me how I can diagnose the exact problem?
2. Can you help me with diagram and explain what do the items circled in yellow mean?
3. Whsy is ignition/start control output means and is it fused before going to WCM? I see it goes to TIPM but where does it go to the WCM?

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post #2 of 33 Old 05-27-2021, 09:30 PM
ColdCase
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Its a code for the wire harness circuit and wire color PK/LG I think is Pink with a light green stripe. S352 identifies a splice. The 20/22 may be wire gage.

The brake switch is three contacts, one connected to the TIPM to activate the brake lights (does your brake lights work?). One contact is used by the PCM during the start sequence (must have foot on brake), and the third contact is used by the PCM for things like cruise control deactivation.

•Brake Lamp Switch Circuit - A normally open brake lamp switch circuit receives a battery voltage input, and supplies this battery voltage to the Center High Mounted Stop Lamp (CHMSL) and the Totallly Integrated Power Module (TIPM) on a brake lamp switch output circuit only when the brake pedal is depressed (brake lamp switch plunger released).

•Brake Lamp Switch Signal Circuit - A normally closed brake lamp switch signal circuit receives a direct path to ground, and supplies this ground input to the Powertrain Control Module (PCM) on a brake signal 1 circuit only when the brake pedal is released (brake lamp switch plunger is depressed).

•Speed Control Circuit - A normally closed speed control circuit receives a battery voltage input from the Totallly Integrated Power Module (TIPM) on an ignition run/start control output circuit, and supplies this battery voltage to the PCM on a brake signal 2 circuit only when the brake pedal is released (brake lamp switch plunger is depressed).

The PCM sends electronic brake lamp switch status messages to other electronic modules in the vehicle over the Controller Area Network (CAN) data bus for use as an additional logic input for controlling many other vehicle functions and features.


So you could try bypassing the speed control contact with a jumper and see if the speed control works. If not, you'll need to verify 12VDC is there when the ignition is on, and circuit continuity back to the PCM.

You cruise control is basic or adaptive (with RADAR) ?

I'll have to doublecheck if there are other conditions where the cruise control is disabled.
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I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #3 of 33 Old 05-27-2021, 09:35 PM Thread Starter
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The brake lights work fine, the shifter knob is released when brake is pressed, and car only starts when brake is pressed. So I guess that rules out the brake switch. I have tested the cruise switch in detail and all buttons show working in all modules but ill swap with another one. I guess that is the only option ive got.


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Originally Posted by ColdCase View Post
Its a code for the wire harness circuit and wire color PK/LG I think is Pink with a light green stripe. S352 identifies a splice.

The brake switch is three contacts, one connected to the TIPM to activate the brake lights (does your brake lights work?). One contact is used by the PCM during the start sequence (must have foot on brake), and the third contact is used by the PCM for things like cruise control deactivation.

•Brake Lamp Switch Circuit - A normally open brake lamp switch circuit receives a battery voltage input, and supplies this battery voltage to the Center High Mounted Stop Lamp (CHMSL) and the Totallly Integrated Power Module (TIPM) on a brake lamp switch output circuit only when the brake pedal is depressed (brake lamp switch plunger released).

•Brake Lamp Switch Signal Circuit - A normally closed brake lamp switch signal circuit receives a direct path to ground, and supplies this ground input to the Powertrain Control Module (PCM) on a brake signal 1 circuit only when the brake pedal is released (brake lamp switch plunger is depressed).

•Speed Control Circuit - A normally closed speed control circuit receives a battery voltage input from the Totallly Integrated Power Module (TIPM) on an ignition run/start control output circuit, and supplies this battery voltage to the PCM on a brake signal 2 circuit only when the brake pedal is released (brake lamp switch plunger is depressed).

The PCM sends electronic brake lamp switch status messages to other electronic modules in the vehicle over the Controller Area Network (CAN) data bus for use as an additional logic input for controlling many other vehicle functions and features.
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post #4 of 33 Old 05-27-2021, 09:46 PM
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I think you may have ruled out two of the three brake switch contacts, did you check the speed control contact?.

What model year is your Jeep? The cruise switches are hard wired to the SCCM (steering column control module), you should be able to check the switch status in the SCCM via your scanner. The steering column and brake switch are the two most common faults.

I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #5 of 33 Old 05-27-2021, 10:01 PM Thread Starter
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Mine is 2013 GC. The brake switch for the third goes to signal 2, i have not been able to rule that out. I am not sure how to check connectivity from the switch to the PCM My scanner shows that all cruise control/ speed control buttons work fine and are registered correctly in SAS module as well as PCM module.

How do i rule out the third brake signal?


Quote:
Originally Posted by ColdCase View Post
I think you may have ruled out two of the three brake switch contacts, did you check the speed control contact?.

What model year is your Jeep? The cruise switches are hard wired to the SCCM (steering column control module), you should be able to check the switch status in the SCCM via your scanner. The steering column and brake switch are the two most common faults.
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post #6 of 33 Old 05-27-2021, 10:21 PM Thread Starter
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Well, I gave this a thought couple of time and was trying to straighten up my logic.
  1. Test -1: The Speed Control Circuit of the Brake Switch should have 12V on A3 with ignition and it should be flowing to A4 when pedal is NOT pressed.
  2. Test -2: If 12 V is not present on A3, look into that wiring
  3. Test -3: If 12 V is present on A3 and passed, somehow check if it is making all the way to PCM
  4. Test -4: If 12 V is present on A3 and passed, and is passed to PCM then problem is something else and should scream and bang my head in a wall



Quote:
Originally Posted by ColdCase View Post
Its a code for the wire harness circuit and wire color PK/LG I think is Pink with a light green stripe. S352 identifies a splice. The 20/22 may be wire gage.

The brake switch is three contacts, one connected to the TIPM to activate the brake lights (does your brake lights work?). One contact is used by the PCM during the start sequence (must have foot on brake), and the third contact is used by the PCM for things like cruise control deactivation.

•Brake Lamp Switch Circuit - A normally open brake lamp switch circuit receives a battery voltage input, and supplies this battery voltage to the Center High Mounted Stop Lamp (CHMSL) and the Totallly Integrated Power Module (TIPM) on a brake lamp switch output circuit only when the brake pedal is depressed (brake lamp switch plunger released).

•Brake Lamp Switch Signal Circuit - A normally closed brake lamp switch signal circuit receives a direct path to ground, and supplies this ground input to the Powertrain Control Module (PCM) on a brake signal 1 circuit only when the brake pedal is released (brake lamp switch plunger is depressed).

•Speed Control Circuit - A normally closed speed control circuit receives a battery voltage input from the Totallly Integrated Power Module (TIPM) on an ignition run/start control output circuit, and supplies this battery voltage to the PCM on a brake signal 2 circuit only when the brake pedal is released (brake lamp switch plunger is depressed).

The PCM sends electronic brake lamp switch status messages to other electronic modules in the vehicle over the Controller Area Network (CAN) data bus for use as an additional logic input for controlling many other vehicle functions and features.


So you could try bypassing the speed control contact with a jumper and see if the speed control works. If not, you'll need to verify 12VDC is there when the ignition is on, and circuit continuity back to the PCM.

You cruise control is basic or adaptive (with RADAR) ?

I'll have to doublecheck if there are other conditions where the cruise control is disabled.
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post #7 of 33 Old 05-27-2021, 10:37 PM
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"... you could try bypassing the speed control contact with a jumper and see if the speed control works. If not, you'll need to verify 12VDC is there when the ignition is on, and the circuit continuity back to the PCM." You may find corrosion in the PCM connector.
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I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #8 of 33 Old 06-09-2021, 04:58 AM Thread Starter
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Quote:
Originally Posted by ColdCase View Post
"... you could try bypassing the speed control contact with a jumper and see if the speed control works. If not, you'll need to verify 12VDC is there when the ignition is on, and the circuit continuity back to the PCM." You may find corrosion in the PCM connector.
I verified the wire and voltage for Brake Signal 2. The wire is good and I can hear continuity beep from PCM to the brake switch. The brake switch works fine. The connector A3 has 12V at ignition and does pass it to PCM.

I have noticed that TIPM does not recognise the brake sense. Same for WCM module. The brake signal does not change in these two on pressing the brake. All other modules register brake signal correctly. Any way forward?
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post #9 of 33 Old 06-09-2021, 05:01 AM Thread Starter
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Some screenshots from my scanner
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Screenshot_20210609-204256_ThinkDiag+_1623236425923.jpg   Screenshot_20210609-204116_ThinkDiag+_1623236436853.jpg   Screenshot_20210609-204056_ThinkDiag+_1623236446018.jpg  
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post #10 of 33 Old 06-09-2021, 06:18 AM
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The brake lights work when the brake pedal is depressed so, the TIPM is getting the brake signal via TIPM C7. Dunno if it is also suppose to receive it from the PCM via the CAN bus. The PCM checks brake circuit 1, if it fails then a P0571 DTC should be set. I don't see a DTC for brake 2 but the scanner should provide PCM status for the signals, maybe look in the PCM speed control area for brake 2.

There may be other conditions, like active DTCs, where the PCM disables the cruise control regardless.

I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #11 of 33 Old 06-09-2021, 11:17 PM Thread Starter
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Quote:
Originally Posted by ColdCase View Post
"... you could try bypassing the speed control contact with a jumper and see if the speed control works. If not, you'll need to verify 12VDC is there when the ignition is on, and the circuit continuity back to the PCM." You may find corrosion in the PCM connector.
Quote:
Originally Posted by ColdCase View Post
The brake lights work when the brake pedal is depressed so, the TIPM is getting the brake signal via TIPM C7. Dunno if it is also suppose to receive it from the PCM via the CAN bus. The PCM checks brake circuit 1, if it fails then a P0571 DTC should be set. I don't see a DTC for brake 2 but the scanner should provide PCM status for the signals, maybe look in the PCM speed control area for brake 2.

There may be other conditions, like active DTCs, where the PCM disables the cruise control regardless.
That is the problem. I cannot find a single DTC in the system. I have no clue what to look for.
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post #12 of 33 Old 06-09-2021, 11:32 PM
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Yeah, something awry with brake signal 2 (Speed Control) is not going to set a DTC. With your scanner you should be able to drill down into the PCM and find the speed control signal status.

I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #13 of 33 Old 06-16-2021, 12:16 AM Thread Starter
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Another finding that i did today is that the TPIM has been replaced previously by someone. The TIPM used in the car is from 2011 GC Diesel Limited. Same trim but 2 year old. Do you think I should replace TIPM and see how it goes?

Since the steering column communicates with TIPM via CAN and if I suspect TIPM's CAN is bad then other things should not work as well. However, cruise is the only thing that does not work in the car.

Quote:
Originally Posted by ColdCase View Post
Yeah, something awry with brake signal 2 (Speed Control) is not going to set a DTC. With your scanner you should be able to drill down into the PCM and find the speed control signal status.
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post #14 of 33 Old 06-16-2021, 07:19 AM
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Stranger things can happen, but cruise is controlled entirely by the PCM, the TIPM is not involved at all. It may be more prudent to monitor Brake Signal2 in the PCM and verify it sees it. Monitor the CAN commands received by the PCM, verify it sees the cruise activation. Look for cruise status messages in the PCM (if any).

Otherwise, without any other visibility or data, you could throw parts at it by first replacing the brake switch and then the PCM. But then you could be wasting your money.

I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #15 of 33 Old 06-16-2021, 06:16 PM Thread Starter
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Quote:
Originally Posted by ColdCase View Post
Stranger things can happen, but cruise is controlled entirely by the PCM, the TIPM is not involved at all. It may be more prudent to monitor Brake Signal2 in the PCM and verify it sees it. Monitor the CAN commands received by the PCM, verify it sees the cruise activation. Look for cruise status messages in the PCM (if any).

Otherwise, without any other visibility or data, you could throw parts at it by first replacing the brake switch and then the PCM. But then you could be wasting your money.

Yes, you are right. Unfortunately my scan tool only shows Main Brake Status in the PCM. WHen I look at the speed control schematic it says that the speed control switch goes to the steering control module which then connects to the TIPM on CAN C + and -. Since I can see the speed control switch buttons pressed in all modules (PCM and SAS) it means that the clock spring is fine, the data is going through to TIPM and then to all modules.

I think I will have to book in for the dealer to have a look at the cruise control and especially brake signal 2.
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