Testing the pre glow system - ra15006024000x(4000)
A. Without after glow, B. With after glow Engines 602.96, 603.96/97 TURBO (Model 463.3: for deviations see introductory notes)
Preceding work:
Operation no. of operation texts and work units or standard texts and flat rates: 15-4000
- Without afterglow
Engine 603.96, except
Model Year 1988
Testing
Testing Glow Lamp and Its Wiring
If the following complaint is received:
Preglow indicator lamp does not light up when preglow system switched on, despite it being possible to start engine.
Detach 4-pin connector from preglow time relay, turn key into position "2", bridge contacts 1 and 3 of the connector. If the preglow indicator lamp does not light up, test glow lamp or renew if necessary.
If the glow lamp is in order, test the black cable from connector contact 3 of the preglow time relay to the preglow indicator lamp for interruption. Rectify interruption. If the preglow indicator lamp lights up, the preglow time relay is faulty. Renew preglow time relay.
COMMERCIALLY AVAILABLE TESTERDesignation e. g. make, order no. Multimeter Sun, DMM-5 Testing Main Circuit of Preglow System for Interruption
If the following complaint is received: Preglow indicator lamp does not light up, engine does not start.
Use the multimeter set to the Volts range to test the voltage at terminal 30 of the preglow time relay to ground.
If no voltage is indicated, test red cable from starter, terminal 30, to the preglow time relay, terminal 30, for interruption. Rectify interruption.
If voltage is indicated (approx. 12 Volts), test 80 ampere fuse for tight fit or interruption; renew if necessary.
If no fault has been found so far, test voltage at contact 1 of the 4-pin connector of the preglow time relay to ground.
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
If voltage is indicated when preglow system is switched on, test pink/red cable from fuse 7 (unprotected side) through plug connection of engine wiring harness to contact 1 of the connector of the preglow time relay for interruption. Rectify interruption.
If voltage is indicated, connect contact 1 (terminal 15) and contact 4 (terminal 31) and test voltage.
If no voltage is indicated, test brown cable from contact 4 to ground for interruption.
Rectify interruption.
If no fault has been detected so far, the preglow time relay is faulty. Renew preglow time relay.
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
Testing glow plugs and wiring
If the following complaint is received:
Preglow indicator lamp does not light up, engine does not start easily, there may be an interruption of one or several glow plugs or of the cables to the glow plugs.
If the following complaint is received:
Preglow indicator lamp lights up, when ready to start condition is reached, engine does not start easily, there may be an interruption of a glow plug or of a cable to the glow plugs of cylinders 2-5, or the cause may be incorrect current consumption of the glow plugs in cylinders 1-6.
Use the multimeter set to the Ampere range and the D.C. clamp to test the current consumption of the glow plugs. This is done by placing the clamp over the individual cables at the preglow time relay.
Cylinder 1 = 2.5 black/blue
Cylinder 2 = 2.5 black/violet
Cylinder 3 = 2.5 black/red
Cylinder 4 = 2.5 black/yellow
Cylinder 5 = 2.5 black/green
Cylinder 6 = 2.5 black/white
Turn the key in the steering lock to position "2"; the current consumption of each glow plug must be 8-15 amperes after 10-20 seconds.
If the reading is higher than 15 amperes, renew the glow plug. If the reading is less than 8 amperes, test electric cable or plug for interruption.
Detach the 6-pin connector from the preglow time relay to test for interruption.
With the multimeter set to the Ohms range, measure in turn the resistance to ground (engine block) as follows:
1 Connector = glow plug cylinder 1
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.
If ∞ Ω resistance is measured, there is an interruption of the respective glow plug or of the lead or of the connection. Rectify interruption in the lead or renew glow plug.
NOTE: It is possible that the indicator lamp does not indicate a fault (because of unfavorable tolerances) until 2 glow plugs in cylinders 2-5 have failed.To check that the fault indication in the preglow time relay is not faulty, 2 glow plugs of cylinders 2-6 should be terminated in this case and the preglow operation repeated. Additionally, on Engine 603, test the fault indication of No. 6 cylinder. This is done by terminating only the glow plug of No. 6 cylinder. If the indicator lamp now shows a fault (does not light up), the preglow time relay is in proper order.
- With afterglow
Engine 602.96, 603.96/97
NOTE: Safeguarding preglow circuit
An electronic short-circuit safeguard is installed in the preglow time relay. The circuit is interrupted if a short-circuit develops in the glow plugs or in the cables.The relay is again operational
- once the short-circuit has been rectified and
- the key is turned back to position "0".
Symbols which are used for the two 6-pin couplings:
Coupling with the pins T, 31, 50, 15, LA:
Coupling with the pins G1-G6:
COMMERCIALLY AVAILABLE TESTERDesignation e. g. make, order no. Multimeter Sun, DMM-5 Test program
COOLANT AND INTAKE AIR TEMPERATURE SENSORSTemperature in °C Resistance (± 10 %) Voltage in V (± 10 %) 20 2.5 kΩ 3.85 30 1.7 kΩ 3.47 40 1.18 kΩ 3.05 50 833 Ω 2.63 60 600 Ω 2.22 70 440 Ω 1.85 80 327 Ω 1.5 90 243 Ω 1.22 100 185 Ω 0.99