97-98 MARK VIII AIRBAG SRS MODULE

97‐98 MARK VIII AIRBAG SRS MODULE Fault Code 51 Fault
Code 51 ‐ Diagnostic Monitor Diagnostic Monitor
Internal Thermal Fuse ‐ Open Due to Intermittent Short To Ground
Intermittent Short To Ground Tech Tip by Glitch
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Problem Code 51
Out of the blue my 1998 Lincoln Mark VIII SRS airbag indicator started to continuously flash code 51. the following is my findings and fix.
The first place I checked was the web; and it listed the SRS code 51 as a “Diagnostic Monitor Internal Thermal Fuse; Open Due to Intermittent Short To Ground “. The web also says that the clockspring is the most probable cause of the short, which opens the thermal fuse that is inside the Diagnostic Monitor. the thermal fuse are designed to fail once a fault is detected over an extended period of time providing protection to the system from an inadvertent deployment . However I could not find any fault with my clockspring even after taking it apart (7 8)
clockspring even after taking it apart. (7, 8)
If you open the Diagnostic Monitor (9, 10, 11) you'll see a black and white component labeled P/n F2DF14A094AA. If you remove this cover, you will find a gray 15 ohm resistor and the silver thermal fuse directly above. The gray resistor is thermally coupled to the fuse allowing heat to be transferred to the fuse. If the fuse gets to hot, the fuse element melts , opening up a circuit causing Code 51 to be displayed.
The thermal fuse that I can tell has a temperature rating of 168 Celsius. Doing a quick search I found www.goodmans.net that sells a fuse one degree shy. (167 Celsius) Because of mail order only, I tried a thermal fuse that can be found locally. Radio Shack has a 140 Celsius fuse.
thermal fuse that can be found locally. Radio Shack has a 140 Celsius fuse.
Even though this fuse is slightly larger then the original. I was able to heat sink it by wrapping the resistor and fuse with copper tape found at any craft store that has stain glass supplies. Note: These fuses are temperature sensitive.... So use heat sinks when installing and don’t leave the soldering iron on them too long.
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Manual fault Isolation
Because I could not find a good schematic; I pieced one together. 3
FAULT INDICATION‐‐AIR BAG INDICATOR FLASHES FAULT CODE 51‐‐PROBABLE FAULT‐‐LOSS OF BATTERY POWER TO AIR BAG FIRING CIRCUIT C1 DEACTIVATE SYSTEM
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Clockspring check:
–
–
–
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PINPOINT TEST C1: –
–
–
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Check Engine Compartment fuse No. 15, 10 amp
• Is fuse open?
• Yes replace fuse
Y
l
f
• No GO to C3
PINPOINT TEST C3: –
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Deactivate system
Disconnect diagnostic monitor
Measure voltage from diagnostic monitor connector Pin 13 (+) (Circuit 609, O/V) to PIn 3 (‐) (57, BK)
• Is voltage greater than 10 volts? • Yes REPLACE diagnostic monitor. VERIFY system. REACTIVATE system
• No GO to C2
PINPOINT TEST C2: –
•
Deactivate system
Remove the following,: diagnostic monitor, steering wheel air bag, stick a piece of plastic strip between the shorting strap and pins at connector for the diagnostic monitor
• Measure pin 10 or 11 to ground pin 3 or 5
• Don’t forget to turn the steering wheel, intermittent faults often show up with movement.
CHECK FOR SHORT TO GROUND IN CIRCUIT 609 (O/V) • Measure resistance from diagnostic monitor connector Pin 13 (Circuit 609, O/V) to ground
• Is resistance less than 10 ohms? • Yes LOCATE and SERVICE short to ground in Circuit 609 (O/V). REPLACE open fuse. RECONNECT system. VERIFY system. REACTIVATE Yes LOCATE and SERVICE short to ground in Circuit 609 (O/V) REPLACE open fuse RECONNECT system VERIFY system REACTIVATE
system. • No GO to PINPOINT TEST C4: –
CHECK FOR SHORT TO GROUND IN CIRCUIT 611 (W/O)
• Measure resistance from diagnostic monitor connector Pin 15 (Circuit 611, W/O) to ground
• Is resistance less than 10 ohms? • Yes GO to
• No GO to
Tech Tip by Glitch
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FAULT INDICATION‐‐AIR BAG INDICATOR FLASHES FAULT CODE 51‐‐PROBABLE FAULT‐‐LOSS OF BATTERY POWER TO AIR BAG FIRING CIRCUIT C1 DEACTIVATE SYSTEM
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PINPOINT TEST C5: –
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PINPOINT TEST C6: –
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VERIFY SHORT TO GROUND IN LH B‐PILLAR SAFING SENSOR
• Measure resistance from LH B‐pillar safing sensor connector Circuit 611 (W/O) and Circuit 612 (P/O) to ground
• Is resistance less than 10 ohms for either circuit? • Yes REPLACE LH B‐pillar safing sensor. REPLACE open fuse. RECONNECT system. VERIFY system. REACTIVATE system
• No INSPECT for crossed wires at LH B‐pillar safing sensor connector and diagnostic monitor connector. SERVICE Circuit 611 (W/O) and/or Circuit 612 (P/O). REPLACE open fuse. REACTIVATE system
PINPOINT TEST C8: –
–
–
•
CHECK FOR SHORT TO GROUND IN CIRCUIT 612 (P/O)
• Measure resistance from diagnostic monitor connector Pin 23 (Circuit 612, P/O) to ground
Measure resistance from diagnostic monitor connector Pin 23 (Circuit 612 P/O) to ground
• Is resistance less than 10 ohms? • Yes LOCATE and SERVICE short to ground in Circuit 612 (P/O). REPLACE open fuse. RECONNECT system. VERIFY system. REACTIVATE system.
• No GO to PINPOINT TEST C7: –
•
CHECK FOR SHORT TO GROUND IN LH B‐PILLAR PANEL SAFING SENSOR • Disconnect LH B‐pillar safing sensor. • Measure resistance from diagnostic monitor connector Pin 15 (Circuit 611, W/O) to ground.
•
Is resistance less than 10 ohms? • Yes LOCATE and SERVICE short to ground in Circuit 611 (W/O). REPLACE open fuse. RECONNECT system. VERIFY system. REACTIVATE system. • No GO to
CHECK FOR INTERMITTENT SHORT TO GROUND
CHECK FOR INTERMITTENT SHORT TO GROUND
Replace open fuse. Reconnect diagnostic monitor. Did fuse open again? • Yes REPLACE Diagnostic monitor. REPLACE open fuse. VERIFY system. REACTIVATE system. • No INSPECT intermittent short to ground in Circuits 937 (R/W), 611 (W/O) and 612 (P/O). SERVICE circuits as required. RECONNECT system. VERIFY system. REACTIVATE system. PINPOINT TEST C9: –
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CHECK FOR PROPER BATTERY VOLTAGE
Measure voltage of vehicle battery
Is voltage less than 10 volts? • Yes RECHARGE vehicle battery. RECONNECT system. VERIFY system. REACTIVATE system. • No LOCATE and SERVICE open in Circuit(s) 937 (R/W) and/or 38 (BK/O). RECONNECT system. VERIFY system. REACTIVATE system.
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Don’tt forget to Bypass Shorting Bars
Don
forget to Bypass Shorting Bars
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