2003 G500 Front Seat Heater Issue
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2003 G500 (W463)
2003 G500 Front Seat Heater Issue
Finally got cold enough in AZ to turn on front seat heaters yesterday. Discovered they don't work! Did the usual troubleshooting and checked the fuses. Found the 30A fuse blown (spot 25 in driver's side dashboard fuse block). As soon as I inserted new fuse, it blew! Obviously, there is a short somewhere in that circuit. Did some searching on this and other websites but unable to find a wiring diagram to determine which wires under the seats are for the seat heaters. Noted that the rear seat heaters work fine. Also noted the rear seat heater fuse is only 7.5A. Anyone have a wire diagram for the front seat harness? Can anyone tell me why the front seat heaters are on a 30A fuse and the rears are only 7.5A?
Appreciate any help!
Appreciate any help!
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2003 G500 (W463)
No solution yet. Still trying to find a detailed wiring diagram of the fuse box and seat heaters. I believe there is a short in the line somewhere before the seat controller. When I disconnect the power to the seat controllers (under the driver's and passenger's seats) and attempt to replace the seat heater 40A fuse, the fuse still blows immediately when installed. Very difficult to troubleshoot without knowing where the wires run.
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No solution yet. Still trying to find a detailed wiring diagram of the fuse box and seat heaters. I believe there is a short in the line somewhere before the seat controller. When I disconnect the power to the seat controllers (under the driver's and passenger's seats) and attempt to replace the seat heater 40A fuse, the fuse still blows immediately when installed. Very difficult to troubleshoot without knowing where the wires run.
Edit: Not sure I understood your information when I posted the above paragraph. If you're saying that the fuse still blows when the seat controller is disconnected then the problem is between the fuse block and controller. The controller comprises a high current capacity switch - probably a relay - that is controlled by a low current activation switch. It seems unusual that a wrapped and secured cable would short out, but still possible. I would have suspected the controller to be at fault, if not the heater element.
Last edited by streborx; Nov 11, 2020 at 09:35 AM.
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2003 G500 (W463)
streborx,
Thanks for the suggestion. Yes, the fuse still blew immediately when I disconnected what I thought was the seat heater power. However, I will attempt your suggestion this afternoon with ALL the cables off both seats. I, too, am surprised a wiring harness would short out.
Another interesting thing is the driver's side electric headrest motor will not run when there is weight on the seat bottom. If I stand outside the car, the headrest will move properly. If I sit in the seat, the headrest will not run. I'm beginning to think something is being pinched in the driver's seat connections.
Again, thanks for the help. I'll let you know what I found later today. (Wife is driving the G-wagen right now!)
Thanks for the suggestion. Yes, the fuse still blew immediately when I disconnected what I thought was the seat heater power. However, I will attempt your suggestion this afternoon with ALL the cables off both seats. I, too, am surprised a wiring harness would short out.
Another interesting thing is the driver's side electric headrest motor will not run when there is weight on the seat bottom. If I stand outside the car, the headrest will move properly. If I sit in the seat, the headrest will not run. I'm beginning to think something is being pinched in the driver's seat connections.
Again, thanks for the help. I'll let you know what I found later today. (Wife is driving the G-wagen right now!)
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2003 G500 (W463)
All the wiring under the seat should have connectors to facilitate seat removal (which might be necessary for heater repair). Disconnect everything, then install a new fuse and reconnect the wiring one connector at a time, checking the fuse after each reconnect. When the fuse blows you'll know which set of wires goes to the heater. If the fuse blows even with everything disconnected, the short is somewhere in the wiring between the fuse block and connector - not a difficult fix but requiring some digging. More likely the heating element in the seat is faulty from being sat on for many years. Then you can decide how much a warm bum is worth.
Edit: Not sure I understood your information when I posted the above paragraph. If you're saying that the fuse still blows when the seat controller is disconnected then the problem is between the fuse block and controller. The controller comprises a high current capacity switch - probably a relay - that is controlled by a low current activation switch. It seems unusual that a wrapped and secured cable would short out, but still possible. I would have suspected the controller to be at fault, if not the heater element.
Edit: Not sure I understood your information when I posted the above paragraph. If you're saying that the fuse still blows when the seat controller is disconnected then the problem is between the fuse block and controller. The controller comprises a high current capacity switch - probably a relay - that is controlled by a low current activation switch. It seems unusual that a wrapped and secured cable would short out, but still possible. I would have suspected the controller to be at fault, if not the heater element.
Thanks for any help!
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The seat heater button and indicator light are on a separate circuit, and probably route to one of the ECUs (I'm guessing the button is push-on/push-off, and the heater has an auto shutoff after 10-15 minutes). The wire on the load side of the 30A fuse likely has a large diameter and a color code (probably a solid color with a striping color), and this should help tracing it through the cable maze.. With the fuse pulled, you might want to verify that the load side of this fuse position is shorted to ground. If you have a volt-ohmmeter, measure the resistance from this fuse output to any chassis point (almost any metallic surface or bolt will be chassis ground). A very low resistance reading (less than an ohm) confirms the wire is shorted to ground. This measurement isn't necessary, but once you're certain the wire is shorted to ground, you know what to look for -- probably chafed insulation in a location where the cable is close to the vehicle's metal framework. Wiring diagrams often specify where to find boxes, controllers, actuators, etc., but seldom indicate where a wire bundle is routed, so a wiring diagram isn't going to be much help troubleshooting this. So all you can do is use a flashlight, telescoping mirror and forceps to trace the wire routing and inspect it cm by cm. From this fuse panel in the dash, likely the wire routes down the foot-well sidewall, along the bottom door frame and up under the seat. Use a plastic pry-bar to pull back the trim pieces and carpet bit by bit until you find something suspicious. Good luck!
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2003 G500 (W463)
The seat heater button and indicator light are on a separate circuit, and probably route to one of the ECUs (I'm guessing the button is push-on/push-off, and the heater has an auto shutoff after 10-15 minutes). The wire on the load side of the 30A fuse likely has a large diameter and a color code (probably a solid color with a striping color), and this should help tracing it through the cable maze.. With the fuse pulled, you might want to verify that the load side of this fuse position is shorted to ground. If you have a volt-ohmmeter, measure the resistance from this fuse output to any chassis point (almost any metallic surface or bolt will be chassis ground). A very low resistance reading (less than an ohm) confirms the wire is shorted to ground. This measurement isn't necessary, but once you're certain the wire is shorted to ground, you know what to look for -- probably chafed insulation in a location where the cable is close to the vehicle's metal framework. Wiring diagrams often specify where to find boxes, controllers, actuators, etc., but seldom indicate where a wire bundle is routed, so a wiring diagram isn't going to be much help troubleshooting this. So all you can do is use a flashlight, telescoping mirror and forceps to trace the wire routing and inspect it cm by cm. From this fuse panel in the dash, likely the wire routes down the foot-well sidewall, along the bottom door frame and up under the seat. Use a plastic pry-bar to pull back the trim pieces and carpet bit by bit until you find something suspicious. Good luck!
Thanks again for the suggestions. I'll report the findings once I've done a bit of wiring archeology.
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2003 G500 (W463)
Did some wiring archeology and believe I found the wire to the load side of the fuse. It is red with a green stripe. i measured the resistance of that side of the fuse block and it is essentially zero. The circuit appears to be shorted to ground. However, from what I can tell the wire bundle doesn't run down the foot-well into the door sill. It runs across the firewall to the center console and down the driver's side of the console into the seat area. I did not measure the continuity from end to end of the wire (because I forgot!) but since there are connectors between it maybe a difficult task.
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From: Colorado
G550
Did some wiring archeology and believe I found the wire to the load side of the fuse. It is red with a green stripe. i measured the resistance of that side of the fuse block and it is essentially zero. The circuit appears to be shorted to ground. However, from what I can tell the wire bundle doesn't run down the foot-well into the door sill. It runs across the firewall to the center console and down the driver's side of the console into the seat area. I did not measure the continuity from end to end of the wire (because I forgot!) but since there are connectors between it maybe a difficult task.
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2003 G500 (W463)
Thanks! The contortionist positions required to do this wire chase may not be worth the effort. Gonna spend an hour in the hot tub tonight after the under dash escapades today. BTW, good TV series!
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2003 G500 (W463)
Dug back into the seat heater issue by checking continuity of the load wire from the fuse block to the first visible under seat connector. According to my ohmmeter, the wire has good continuity across that length. I also measured from pin-to-pin in the connector and it also shows OK.
Looks like I have to pull the seats to chase the wire inch-by-inch looking for the short/chafed area. It will require a lot of carpet pulling and panel removal. Not really willing to do that myself so I'm dropping it at my independent repair shop tomorrow. Will update when I get the car back.
Looks like I have to pull the seats to chase the wire inch-by-inch looking for the short/chafed area. It will require a lot of carpet pulling and panel removal. Not really willing to do that myself so I'm dropping it at my independent repair shop tomorrow. Will update when I get the car back.
MBWorld Fanatic!
Joined: Oct 2019
Posts: 5,152
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From: Colorado
G550
Dug back into the seat heater issue by checking continuity of the load wire from the fuse block to the first visible under seat connector. According to my ohmmeter, the wire has good continuity across that length. I also measured from pin-to-pin in the connector and it also shows OK.
Looks like I have to pull the seats to chase the wire inch-by-inch looking for the short/chafed area. It will require a lot of carpet pulling and panel removal. Not really willing to do that myself so I'm dropping it at my independent repair shop tomorrow. Will update when I get the car back.
Looks like I have to pull the seats to chase the wire inch-by-inch looking for the short/chafed area. It will require a lot of carpet pulling and panel removal. Not really willing to do that myself so I'm dropping it at my independent repair shop tomorrow. Will update when I get the car back.
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2003 G500 (W463)
You, sir are correct! The continuity across the length of cable looks just like a short to ground: zero ohms ( or nearly so). I gave all my troubleshooting info to my indy shop and they're gonna go from there. Personally, I believe the short is before the seat connector where the cable makes multiple direction changes under the carpet. This also is an area where rear seat passengers feet move about. More words to follow in a few days.
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You, sir are correct! The continuity across the length of cable looks just like a short to ground: zero ohms ( or nearly so). I gave all my troubleshooting info to my indy shop and they're gonna go from there. Personally, I believe the short is before the seat connector where the cable makes multiple direction changes under the carpet. This also is an area where rear seat passengers feet move about. More words to follow in a few days.
