JensenHealey
Member
Hello all
I have a 1993 Mercedes 300TE with the 3.2L DOHC M104 engine. It is a 2wd base model, not the 4Matic type of car. I have been working on the car for some time to revive it from an extended dry storage by the previous owner.
I have pretty much everything done except for a problem with the ABS light on the dash being illuminated 100% of the time once the car is started.
Without moving the car or pressing the brake pedal, once the car is started the ABS light comes on and never goes out.
I have done a lot of research and reading on this issue. The car has the 16 port trouble code breakout box in front of the battery but does not have the light and button built into this box to allow the ability to see the pulse or blink codes without any additional equipment.
I have looked at the over voltage protection relay and ran various tests as outlined below that are applicable to a 9 pin single fuse OVP relay:
Pin 1 should be connected to the positive battery terminal (12v), and Pin 5 should be connected to the negative battery terminal. Check for voltage at all the remaining pins. ONLY Pin 9 should have voltage (12v).
With Pins 1 and 5 connected as above, connect Pin 3 to the positive battery terminal. This is like turning the ignition key. You should hear the click of the relay. Now you should have 12v at Pins 9,8,7 and 2. No voltage should be at Pins 4 and 6. However, Pins 4 and 6 should have continuity now.
The OVP relay passed these tests just fine. I also opened up the hydraulic unit by removing the plastic cover held down by the single screw and looked at the two relays under that cover. I tested those two relays as well and they seem to be operating properly.
I used a Volt/Ohm meter and checked the resistance readings of the three speed sensors (one in each front wheel and one in the differential) and got 0.970 ohms for one front wheel sensor and 0.997 ohms for the other. The rear sensor gave a resistance reading of 0.67 ohms. I also checked the two front wheel sensors using the AC volts setting on the meter while spinning each wheel. I got a signal from each sensor when doing this test. One sensor gave a slightly higher reading in this test than the other. I have not yet been able to test the rear speed sensor in the diff using this same AC volt test but I will do that later today.
I am also going to try pulling each front wheel sensor out of the hubs and cleaning them and looking at the toothed wheel inside.
I built a blink code box using an LED and a momentary push button circuit to see if I could pull any pulse codes out of the car but this did not produce any codes related to the ABS system.
Anyone have any other suggestions about things I should be looking at?
I have a 1993 Mercedes 300TE with the 3.2L DOHC M104 engine. It is a 2wd base model, not the 4Matic type of car. I have been working on the car for some time to revive it from an extended dry storage by the previous owner.
I have pretty much everything done except for a problem with the ABS light on the dash being illuminated 100% of the time once the car is started.
Without moving the car or pressing the brake pedal, once the car is started the ABS light comes on and never goes out.
I have done a lot of research and reading on this issue. The car has the 16 port trouble code breakout box in front of the battery but does not have the light and button built into this box to allow the ability to see the pulse or blink codes without any additional equipment.
I have looked at the over voltage protection relay and ran various tests as outlined below that are applicable to a 9 pin single fuse OVP relay:
Pin 1 should be connected to the positive battery terminal (12v), and Pin 5 should be connected to the negative battery terminal. Check for voltage at all the remaining pins. ONLY Pin 9 should have voltage (12v).
With Pins 1 and 5 connected as above, connect Pin 3 to the positive battery terminal. This is like turning the ignition key. You should hear the click of the relay. Now you should have 12v at Pins 9,8,7 and 2. No voltage should be at Pins 4 and 6. However, Pins 4 and 6 should have continuity now.
The OVP relay passed these tests just fine. I also opened up the hydraulic unit by removing the plastic cover held down by the single screw and looked at the two relays under that cover. I tested those two relays as well and they seem to be operating properly.
I used a Volt/Ohm meter and checked the resistance readings of the three speed sensors (one in each front wheel and one in the differential) and got 0.970 ohms for one front wheel sensor and 0.997 ohms for the other. The rear sensor gave a resistance reading of 0.67 ohms. I also checked the two front wheel sensors using the AC volts setting on the meter while spinning each wheel. I got a signal from each sensor when doing this test. One sensor gave a slightly higher reading in this test than the other. I have not yet been able to test the rear speed sensor in the diff using this same AC volt test but I will do that later today.
I am also going to try pulling each front wheel sensor out of the hubs and cleaning them and looking at the toothed wheel inside.
I built a blink code box using an LED and a momentary push button circuit to see if I could pull any pulse codes out of the car but this did not produce any codes related to the ABS system.
Anyone have any other suggestions about things I should be looking at?
