Mecedes 1979 300D glow plugs do not glow

DTC P0671: Cylinder #1 Glow Plug Control Circuit
DTC P0672: Cylinder #2 Glow Plug Control Circuit
DTC P0673: Cylinder #3 Glow Plug Control Circuit
DTC P0674: Cylinder #4 Glow Plug Control Circuit
DTC P0675: Cylinder #5 Glow Plug Control Circuit
DTC P0676: Cylinder #6 Glow Plug Control Circuit
DTC P0677: Cylinder #7 Glow Plug Control Circuit
DTC P0678: Cylinder #8 Glow Plug Control Circuit

Circuit/System Description
The glow plug controller has the ability to perform internal checks, an open or a short to ground on each of the glow plug circuits. If the glow plug controller senses a problem in a glow plug circuit, the glow plug on the affected cylinder will be disabled and the glow plug controller will send an error message to the engine control module (ECM). If this condition exists, the DTC will set.
Conditions for Setting the DTC
The glow plug controller detects that the glow plug control circuit is open, shorted to ground, or has more than 1 ohm of resistance.

Circuit/System Verification
Verify that DTC P064C is not set.
If DTC P064C is set, refer to DTC P064C.
Ignition ON, engine OFF, observe the scan tool Glow Plug 1-Glow Plug 8 parameters. All 8 Glow Plug parameters should closely match each other.
Refer to Testing for Intermittent Conditions and Poor Connections if you cannot duplicate the conditions.
Engine running, observe the DTC information with a scan tool. DTCs P0671-P0678 should not set.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

DTC C0035 Left Front Wheel Speed Sensor Circuit
DTC C0201 Antilock Brake System (ABS) Enable Relay Contact Circuit
The system relay, located within the electronic brake control module (EBCM), supplies battery voltage to all of the valve solenoids and to the ABS pump motor. When the relay contacts close, the EBCM monitors the voltage supplied to the valve solenoids and compares this voltage to monitored ignition voltage.

Try changing No1 glow plug with No 2 and see if the code changes, if it does you may well have a faulty new plug ( it happens frequently with the non genuine products )Regards Mike

glow pug indicator and glow plug themself are 2 seperate system
test for power at the glow plug harness conector 1 each side over valve cover
test light clamp on batery neg test each wire going to relay for power on both side
then quick check on glow plug end test light clamp on positive test all wires
going to glow pug on each side f this does ligtht up the test light system should be o.k.
for the FICM i have used a hair blower on hi to warm the surface of if to start up a few of
these motors to get them back to the yard for replacment afterward
run a ffeet of these from 250 to 550 lots of problem and work 26 units
good luck

should be handy enough just screw out put new one in
if your machine hard to start when heating in the morning ,wait twenty seconds after light goes out then crank it
heater relay still working when heat indicator light goes out

Have you checked the glow-plugs? On that system if one glow-plug is burnt up than it will not let the main relay in the controller to kick in.
Check all the glow-plugs make sure they are working.
The easiest way to check them is with a regular 12v test light.
Hook up the negitive end (aligator clip end ) to the battery + terminal and than with the other end of the test light ( pointed end ) touch each glow- plug connector tip ( with the glow-plugs harness connector removed ) and see if the test light lights up.
If the test light up--- glow-plug is good. If not than the glow-plug is bad--burnt out .

HI. This is an indication of a failing glow plug. It will be necessary to test each plug to isolate the issue, or run a diagnostic scan on the CPU. During the scan, you should be issued a code that will isolate the actual glow plug that is malfunctioning. If you insist on testing each plug, use my procedure below to assist. You can find the resistance specs in your operators manual.


A test light can be used to determine if the glow plugs are working.


1. With the test-light grounded, insert the test light probe into a glow-plug wire to check for continuity.

2. If the light comes on, check the other cylinders in the same manner. If the test light failed to light, check for continuity at the glow-plug relay.

3. If no power is present, check the control circuit of the glow plug relay.

4. If the control circuit is working, the relay may be defective (FYI, manufacturers may have the system fused and fusible links may be located throughout the system).

5. If the glow-plug circuit is working, the glow plugs themselves may be defective.

Checking glow-plug resistance:(Remove the plug for this test)

1. With an ohmmeter, connect one lead to the terminal and the other lead to the body.

2. Read the resistance and compare to specifications.

3. A visual inspection may also be necessary to check for excessive carbon buildup and physical damage to the tip.

4. A glow plug that has excessive carbon deposits on its tip can give the correct ohmmeter reading but still not work. Clean the tip with carbon cleaner.(DO NOT USE A BRUSH TIP CLEANER)

The glow plug relay is responsible for the duration of glow plugs, this needs to be the starting point. You should get a 12v out for so many seconds when ignition is switched on.
I have taken the cover off relays in the past, cleaned up the internals, sprayed with circuit cleaner and got plenty more years out of them, worth a try.

Has glow plugs --check them. you can use a 12v test light or an volt/ohm meter to test each plug. Disconnect the connector on the glow-plug ,then and touch with a 12v test light --one lead to a12v supply.If the test light lights up that plug is good. or with a volt/ohm meter ,one lead to ground and the other touching the tip of a glow-plug--that's on the ohm's scale --if it reads --showing continuity,then that plug is good.
If all check good you may have a bad glow-plug controller.

this is a common problem for these cars glow plugs go bad like spark plugs however the smoke would lead to bad mass airflow meter. it is not telling ecu corrcet miss. disconnect mass airflow meter. when cold see if this makes it start better. it should would means you need new m.a.f. glow plug issue take a test light place clamp on positive of battery then pull off glow plug connectors place tip of test light on glow plug the bad one will have a dull light unlike the good one which will be brighter. will need new plugs and wire harness four **** connectors and wire striper and crimper will fix concern good luck

the best way i have found to test glow plugs is to disconnect the wire to the plug and get you 12volt test light and put your negitive lead of the test light on the positive battery cable so when you touch the test light to any ground the light will light. so now go check your glow plugs and if you have one that doesnt light the light its burned out.
good luck