A fault that may not be repaired normally
No trouble code
There is no problem with the line
No problem with parts
Can you guess the point of failure?

Failure case

Model: Liuqi
Engine: Cummins
Emission standard: National IV
Computer board: CM2150
Trouble phenomenon: cruise failure

Troubleshooting steps

Step 1: Read the fault code.

The driver reported that the cruise control failed, and there was no cruise related fault code read with the diagnostic instrument.

Maintenance analysis:

Do not worry about repairing the car, and have a clear idea. First, we must analyze the reasons for cruise failure:
1. The cruise switch is damaged
2. There is a problem with the cruise to the ECU circuit
3. Depress the clutch pedal or brake pedal
4. Speed is too high or too low, etc.

Step 2: Read the data stream.

After knowing the cause of the failure, you can prescribe the right medicine.
I read the data stream related to cruise with a diagnostic instrument, and found that the switch and up/down gears were normal, and the only abnormal shop was on the brake pedal. During the time limit in the data stream, the state of the brake pedal is always depressed, then after the ECU receives this signal, the cruise will definitely not work.

Maintenance analysis:

Let’s continue to analyze the wave, what are the reasons that cause the brake pedal to be depressed:
1. The brake pedal position sensor is damaged
2. Unreasonable installation of brake pedal position sensor
3. Line problems

Step 3: Check the brake pedal.

First check the brake pedal position sensor. This car has a brake light switch and brake pedal position. The sensors are separate, so don’t get confused.

In addition, if the brake light switch has been replaced, improper installation will also cause the brake pedal to be displayed continuously.
Check that the brake light switch is installed correctly.

But the adjustment cam of the brake pedal sensor is relatively loose, and the problem lies here!

Adjust the cam to a proper position and tighten it, read the data stream again to display the release, and the problem is solved.

The driver tests the car, communicates by phone, and cruises at a constant speed.

Summary

For this kind of EFI vehicle, the first thing to do to maintain the cruise control is to read the relevant data stream first, so that the solution will be faster and more accurate.

Knowledge development

What is cruising

Cruising means that when the driver releases the accelerator, the engine controls the vehicle to run at the speed set by the driver.

Cruise can reduce the workload of the driver and improve the driving performance of the vehicle. It can also optimize parameter settings, improve economy and improve vehicle performance.

The principle is actually very simple. After the driver sets the speed, the engine controls the fuel supply to keep the speed constant.

How to use cruise

Take Sinotruk as an example:

1. When the vehicle reaches the desired speed (generally greater than 30km/h), press “Cruise+” (SET/+) or “Cruise-” (SET/-) to enter the cruise mode, and the cruise indicator will light up.

2. When in the cruise state, if you press “Cruise+” once, the vehicle speed will increase by 3km/h; if you press “Cruise-” once, the vehicle speed will decrease by 3km/h. If you continue to press “Cruise +” or “Cruise -” for a long time, the vehicle speed will continue to change.

3. The normal use of cruise also needs to meet the following conditions:

(1) The brake pedal is released;

(2) Release the clutch pedal;

(3) Gearbox is in gear;

(4) Release the accelerator pedal;

(5) The engine brake is not connected.

4. Conditions for exiting cruise: depressing the brake pedal, continuously depressing the clutch, continuously depressing the accelerator, etc.

Cruise failure detection

1. Line failure

(1) There is a problem with the vehicle speed received by the ECU, which can be judged by reading the vehicle speed with a diagnostic instrument;

(2) The cruise common terminal is short-circuited or short-circuited to ground. You can use a multimeter to check the conduction of the cruise switch to the clock spring, the clock spring to the cab harness assembly, the chassis harness interface, the chassis harness assembly, the cab harness interface, and the ECU wire Pass the situation;

(3) If the clock spring is faulty, you can use the replacement method to check whether the problem is solved;

(4) If the connector is loose, you can visually check whether the connector is loose;

(5) CAN bus communication problem.

2. Abnormal clutch signal

(1) If the clutch switch fails, you can use the replacement method to check whether the problem is solved;

(2) If the connecting and disassembling parts are loose, you can visually check whether the connectors are loose;

(3) If the clutch signal circuit is faulty, you can use a multimeter to check the continuity and voltage of the circuit.

3. Brake signal failure

(1) If the brake switch fails, you can use the replacement method to check whether the problem is solved;

(2) If the connector is loose, you can visually check whether the connector is loose;

(3) If the auxiliary brake signal circuit is faulty, you can use a multimeter to check the continuity and voltage of the brake circuit.

4. Throttle signal failure

(1) If the accelerator pedal is faulty, you can replace the accelerator pedal with the replacement method to check whether the problem is solved;

(2) If the connector is loose, you can visually check whether the connector is loose;

(3) The accelerator pedal signal circuit is faulty, you can use a multimeter to check the continuity and voltage of the accelerator pedal circuit.

5. Cruise switch failure

(1) The substitution method can be used to determine whether to solve the problem.

6. ECU problem

(1) The substitution method can be used to determine whether to solve the problem.

Failure case

Troubleshooting steps

Step 1: Read the fault code.

Maintenance analysis:

Step 2: Read the data stream.

Maintenance analysis:

Step 3: Check the brake pedal.

Summary

Knowledge development

What is cruising