I am trouble shooting my completely dead cruise control on the 83 300DT
It has the newer electric actuator.
I am following the test procedures here:
Test Procedures - Table of Contents
Here is my way of doing it (so far unsuccesful
First thing I did is test the actuator in the engine bay:
7 engage solenoid
So I disconnected the connector of the actuator and started testing:
I apply +12v and ground on pin 4 and 5 and the motor spins, i reverse the voltage and it spins in the other way so it works.
I apply +12v on pin7 and ground on pin 6 and actuator clicks.
I apply +12V on pin7 and pin5 and apply ground on pin 6 and 4 and solenoid engages and motor starts to pull the throttle linkage. (so it works)
I disconnect the linkage and measure resistance between pin 2 and 3 (this is a potentiometer which resistance changes according to the position of the shaft that pulls the linkages. Now this pot was not working correctly so I took apart the actuator cleaned the pot and after that at Idle it shows about 1-2 Ohm as I push the throttle the resistance increases to a few Kohms.
So conclusion is that the actuator is completely working now.
So then I test the Steering column switch and other signals at the amplifier:
(Whit the amplifier disconnected and ignition on)
At the amplifier (cruise control unit) which is next to the brake pedal:
pin signal connected to actuator
1 Power: 12Vdc
2 Decel/Set (from switch)
3 On/Off (from switch)
4 Accel/Set (from switch)
5 Actuator Engage Solenoid (output) 7 Engage Solenoid
6 Resume (from switch)
7 Motor Control 4 Motor Brush
8 Brake Disengage (brake light bulbs)
9 Actuator Positional Feedback 3 Potentiometer End
10 Motor Control (output) 5 Motor Brush
11 Speed Input (from transducer)
12 Ground 1, 6 Grounds
13 Actuator Positional Feedback 2 Potentiometer Wiper
pin 1 does have the 12v and pin 14 had the ground.
Switch Test (meter common to ground)
Pin 1 BV (BV = battery voltage: somewhere between 12.5 and 13.8 Vdc)
Pin 2 Decel/Set 0 Vdc initially - goes to BV for Decel/Set
Pin 3 On/Off BV initially - goes to 0 V for Off
Pin 4 Accel/Set 0 Vdc initially - goes to BV for Accel/Set
Pin 6 Resume 0 Vdc initially - goes to BV for Resume
Pin 8 Brake Disengage MUST BE 0 Vdc for Cruise System to work - goes to BV when you step on the brake.
The system gets a critical ground through the brake light bulb filaments. If both bulbs are burned out or there is not proper ground here the system will not work. This is the mechanism for cancelling the Cruise when you step on the brake: this pin goes from ground to plus voltage and loses a ground which is necessary for the sytem to stay engaged.
Pin 12 Ground
Pin 14 Ground (some cars have no ground here; the system will work without it)
So tested all that and got the right results and yes Pin 8 is 0V and when I press the brakes it goes to +12v.
So this proves that the brakes switch works + control switch on steering wheel works.
I also did this test with actuator connected and amplifier disconnected and measuring on the amplifier connector:
From Pin To Pin Actuator Amplifier Resistance
Number Number Plugged in? Plugged in? in ohms
7 10 yes no 3 to 30 ohms (not 0 ohms!)
7 gnd (12) yes no infinity
10 gnd (12) yes no infinity
5 gnd (12) yes no infinity 002 545 86 32 (or) ~40 ohms 001 545 75 32
9 gnd (12) yes no 3.4 K ohms ±0.6 K ohms
9 13 yes no 0 ohms approx.
on pin 7 to 10 - got 4 ohm, the other 2 got infinity, on pin 5 to 12 got 40 ohm
on pin 9 to 12 got about 3k ohm, on pin 9 to 13 got about 2-3 ohm and when i press the throttle it increases.
So the conclusion:
Steering column switch works,
Actuator in the engine bay works, (I did have to clean the pot)
The connecting cables are intact and work,
break disengage works correctly.
Went for a test drive - nothing (completely dead)
And NO - it is not the fuse, first I have checked it and second there will not be +12 v at pin 1 of on the amp connector with ignition on
So the amplifier you will say... ok I took it apart, resoldered it and put it back in - NOTHING. So then went to the junkyard and got another one out of a W126 560SEL and guess what NOTHING.
So the only thing that I have yet to test is this:
B) Speed Sensor Test (meter common to ground)
This test must be performed with the rear wheels turning. Please have two qualified people present at all times.
Pin 11 Speed Sensor loaded (with the amplifier plugged in) must be at least 2.0 Vrms at 25 mph.
The amplifier actually measures the frequency of this signal. At 60 mph the frequency should be 131 Hz.
I can not measure the frequency because my multimeter is a cheap one, but I guess I could check to see if there is 2.0 V at 25mph. Or I might get a better multimeter from a friend of mine that can measure frequency.
So the speed sensor is my last hope. Any other ideas will be very appreciated.