For years the red glow of the SRS warning lamp has been my constant driving companion. Shorting the Service Check Connector on the passenger's side yielded a DTC (error code) of 5-1 - "Internal fault in the SRS unit." Clearing this error code with the Memory Erase Signal Connector (MES) under the dash only worked until the next time I started the car, when the SRS indicator would illuminate again. Unwilling to pay for a new SRS unit, I just lived with it, uncertain whether or not the airbags would deploy in an accident.
Last week my car failed to start due to a dead battery. I replaced the battery - it was 8 years old - and when I started the car the SRS light went out. That was the first time in four years that the SRS light stayed off while the car was running.
Why would a new battery cause the SRS light to go out? Curious, I discovered in the Service Manual (Helm) and in Honda Service News (November 1997) that low battery voltage or problems with the charging system can cause the 5-1 or 9-2 internal SRS module errors. Apparently, the SRS module self-check procedure has stringent voltage thresholds, and values above or below these strict limits can trigger an error code. Even a battery good enough to start the Odyssey through years of harsh Michigan winters had not been good enough to meet the SRS voltage requirements.
[From the service manual: "When you keep the ignition switch turned ON (II) or keep the engine cranking with low battery voltage (discharged battery), this may be self-diagnosed as a failure in the SRS system, and the SRS indicator light may indicate...DTCs 9-2, 5-1." From Honda Service News 11/97: "A battery that's not fully charged can set an SRS DTC. In the S/M, these DTCs are listed as an 'Internal failure of the SRS unit,' but low battery voltage can also cause them."]
Of course, "Internal failure of the SRS unit" is a misleading term for an error really caused by low battery voltage rather than a faulty SRS module. Honda Service News recommends testing the battery and charging system as the first step in diagnosing these errors. (I wonder how many SRS modules have been replaced when the real culprit was a bad battery?)
The happy ending to my 4 year SRS saga was spoiled a couple days after I replaced the battery when I realized that the SRS light wasn't illuminating at all - even during the initial ignition-on test period. Apparently the SRS indicator bulb had burned out right after I replaced the dead battery. So had I really done anything to cure the SRS problem, or was I just deceived by the weird coincidence of failed indicator bulb at the time of battery replacement? To find out, I replaced the SRS indicator bulb and cleared the SRS memory. Much to my relief, the SRS indicator lamp now functioned normally - it illuminated during the initial self-test period and then stayed out after the car was started. So the new battery really had cured the SRS problem after all and the burned out bulb was just a coincidence.
I should mention that my previous attempts - years ago - to clear the SRS indicator light by way of the Memory Erase Signal Connector were misguided and were based upon a misunderstanding of how the SRS indicator lamp functions. I've since realized that in addition to the initial ignition-on period, there are two different kinds of states that can cause the SRS light to be illuminated. One is when the continuous SRS module self-testing process finds an on-going error. The second state is when there is no on-going error found, but a previous stored error code remains in SRS memory. Either one of these two conditions causes the illumination of the indicator light. If the SRS module has found an on-going error, there is no point in clearing the SRS memory register, since the SRS module will immediately re-store the current DTC code in the recently cleared memory. It would be like trying to remove water from a tub while the faucet is still turned on. Whatever you remove is immediately replaced.
The only time it makes sense to clear the SRS memory via the MES connector is when there is no on-going DTC. In this situation the SRS light is illuminated because a copy of an old - now corrected - DTC is still stored in memory. Only under these circumstances will use of the MES turn off the SRS light. What this means is that the MES connector cannot be used to "reset" or "clear" a current error in the SRS module. If an error state exists, nothing you do with the MES will fix it. If the error condition has been corrected, and the old error code persists in memory, then you can use the MES to clear the code from memory and thereby turn off the SRS indicator.
How can you tell if the SRS light is illuminated because of an on-going error or because an old error is still stored in memory? When you short the Service Check Connector, an on-going error will flash in an infinitely repeating loop. (E.g., 9-2, 9-2, 9-2, 9-2, etc, etc, etc.) If there is no on-going error, but an old error code remains in memory, then the DTC will be flashed only once. So, if you run the diagnostic procedure and find a DTC flashing repeatedly, don't bother clearing the SRS memory. You need to fix the cause of the problem before you do anything about clearing the SRS memory. If the DTC flashes only once then you can erase the SRS memory as a means of turning off the indicator light.
Since replacing the SRS indicator bulb wasn't an entirely straightforward process and isn't covered in the Helm manual, I thought I would recount the procedure here:
1) Remove the small vent just to the left of the instrument cluster. Just pull it straight out.
2) Behind the vent you will find one of the three screws holding the instrument cluster cover in place. The other two are found at the inside top of the cluster cover. Remove the cover's three screws.
3) With the instrument cluster cover removed you will see four screws holding the instrument cluster to the firewall/dashboard. Remove these four screws.
4) Carefully pull the gage cluster forward. Now try to locate the SRS bulb. Surprise! There is a tiny circuit board in the place where the bulb should be. Unlike the other dash bulbs, the SRS bulb is mounted on a tiny circuit board. To get to the bulb, first remove the yellow wire connector attached to the back of the small circuit board. The circuit board is held in place by a white plastic tab which pulls out from the main instrument board. Before removing the white plastic tab I removed the three light bulb holders in the area closest to the SRS indicator circuit board. This takes some pressure off the main instrument board's flexible circuit "sheet" and reduces the likelihood that you will tear the circuit sheet as you remove the SRS indicator circuit board. (Since the large flexible circuit sheet partially covers the SRS indicator board, if you aren't careful pulling out the SRS circuit board you may damage the large flexible circuit sheet.)
5) The SRS bulb is similar to the type described in this thread about the Odyssey clock light http://www.odyclub.com/forums/showthread.php?s=&threadid=23429&highlight=climate+lights. I used the same Radio Shack "micro lamp" recommended in that thread. To replace the bulb you need to pull the small square black rubber bulb holder off the two metal prongs on the SRS indicator circuit board. With the rubber bulb holder removed you can extract the old bulb and its wire leads and then insert the new bulb in the bulb holder, being careful to route the wire leads so they will be in contact with the two prongs on the circuit board when you push the rubber bulb holder back in place. I purchased my new bulb at Radio Shack - #272-1092 - for $1.79. My local Honda parts counter didn't have replacement bulbs, but they did offer to sell me a new SRS indicator circuit board with bulb installed for $34.
6) Push the bulb holder with the new bulb down onto the two circuit prongs. Temporarily connect the SRS lighting harness to the SRS indicator circuit board and test the new bulb. It should light for around 6 seconds when the ignition is turned on. (Of course it won't go out after six seconds if the SRS unit discovers an error or if a previous error is stored in the SRS module's memory.)
7) Remove the yellow harness from the indicator circuit board and reinstall the indicator circuit board in the back of the instrument cluster. Install the white tab that locks the SRS indicator board into the back of the instrument cluster. Be careful not to tear the circuit sheet that runs the length of the back of the instrument cluster. Replace any other bulbs in the instrument cluster that you previously removed to facilitate handling the SRS indicator circuit board.
8) Reinstall the four screws holding the instrument cluster to the bulkhead and the three screws holding the cluster cover in place. Install the vent to the left of the cluster - just press it back in place.
That's it!
daneli
1996 Honda Odyssey
2000 Honda Odyssey
Last week my car failed to start due to a dead battery. I replaced the battery - it was 8 years old - and when I started the car the SRS light went out. That was the first time in four years that the SRS light stayed off while the car was running.
Why would a new battery cause the SRS light to go out? Curious, I discovered in the Service Manual (Helm) and in Honda Service News (November 1997) that low battery voltage or problems with the charging system can cause the 5-1 or 9-2 internal SRS module errors. Apparently, the SRS module self-check procedure has stringent voltage thresholds, and values above or below these strict limits can trigger an error code. Even a battery good enough to start the Odyssey through years of harsh Michigan winters had not been good enough to meet the SRS voltage requirements.
[From the service manual: "When you keep the ignition switch turned ON (II) or keep the engine cranking with low battery voltage (discharged battery), this may be self-diagnosed as a failure in the SRS system, and the SRS indicator light may indicate...DTCs 9-2, 5-1." From Honda Service News 11/97: "A battery that's not fully charged can set an SRS DTC. In the S/M, these DTCs are listed as an 'Internal failure of the SRS unit,' but low battery voltage can also cause them."]
Of course, "Internal failure of the SRS unit" is a misleading term for an error really caused by low battery voltage rather than a faulty SRS module. Honda Service News recommends testing the battery and charging system as the first step in diagnosing these errors. (I wonder how many SRS modules have been replaced when the real culprit was a bad battery?)
The happy ending to my 4 year SRS saga was spoiled a couple days after I replaced the battery when I realized that the SRS light wasn't illuminating at all - even during the initial ignition-on test period. Apparently the SRS indicator bulb had burned out right after I replaced the dead battery. So had I really done anything to cure the SRS problem, or was I just deceived by the weird coincidence of failed indicator bulb at the time of battery replacement? To find out, I replaced the SRS indicator bulb and cleared the SRS memory. Much to my relief, the SRS indicator lamp now functioned normally - it illuminated during the initial self-test period and then stayed out after the car was started. So the new battery really had cured the SRS problem after all and the burned out bulb was just a coincidence.
I should mention that my previous attempts - years ago - to clear the SRS indicator light by way of the Memory Erase Signal Connector were misguided and were based upon a misunderstanding of how the SRS indicator lamp functions. I've since realized that in addition to the initial ignition-on period, there are two different kinds of states that can cause the SRS light to be illuminated. One is when the continuous SRS module self-testing process finds an on-going error. The second state is when there is no on-going error found, but a previous stored error code remains in SRS memory. Either one of these two conditions causes the illumination of the indicator light. If the SRS module has found an on-going error, there is no point in clearing the SRS memory register, since the SRS module will immediately re-store the current DTC code in the recently cleared memory. It would be like trying to remove water from a tub while the faucet is still turned on. Whatever you remove is immediately replaced.
The only time it makes sense to clear the SRS memory via the MES connector is when there is no on-going DTC. In this situation the SRS light is illuminated because a copy of an old - now corrected - DTC is still stored in memory. Only under these circumstances will use of the MES turn off the SRS light. What this means is that the MES connector cannot be used to "reset" or "clear" a current error in the SRS module. If an error state exists, nothing you do with the MES will fix it. If the error condition has been corrected, and the old error code persists in memory, then you can use the MES to clear the code from memory and thereby turn off the SRS indicator.
How can you tell if the SRS light is illuminated because of an on-going error or because an old error is still stored in memory? When you short the Service Check Connector, an on-going error will flash in an infinitely repeating loop. (E.g., 9-2, 9-2, 9-2, 9-2, etc, etc, etc.) If there is no on-going error, but an old error code remains in memory, then the DTC will be flashed only once. So, if you run the diagnostic procedure and find a DTC flashing repeatedly, don't bother clearing the SRS memory. You need to fix the cause of the problem before you do anything about clearing the SRS memory. If the DTC flashes only once then you can erase the SRS memory as a means of turning off the indicator light.
Since replacing the SRS indicator bulb wasn't an entirely straightforward process and isn't covered in the Helm manual, I thought I would recount the procedure here:
1) Remove the small vent just to the left of the instrument cluster. Just pull it straight out.
2) Behind the vent you will find one of the three screws holding the instrument cluster cover in place. The other two are found at the inside top of the cluster cover. Remove the cover's three screws.
3) With the instrument cluster cover removed you will see four screws holding the instrument cluster to the firewall/dashboard. Remove these four screws.
4) Carefully pull the gage cluster forward. Now try to locate the SRS bulb. Surprise! There is a tiny circuit board in the place where the bulb should be. Unlike the other dash bulbs, the SRS bulb is mounted on a tiny circuit board. To get to the bulb, first remove the yellow wire connector attached to the back of the small circuit board. The circuit board is held in place by a white plastic tab which pulls out from the main instrument board. Before removing the white plastic tab I removed the three light bulb holders in the area closest to the SRS indicator circuit board. This takes some pressure off the main instrument board's flexible circuit "sheet" and reduces the likelihood that you will tear the circuit sheet as you remove the SRS indicator circuit board. (Since the large flexible circuit sheet partially covers the SRS indicator board, if you aren't careful pulling out the SRS circuit board you may damage the large flexible circuit sheet.)
5) The SRS bulb is similar to the type described in this thread about the Odyssey clock light http://www.odyclub.com/forums/showthread.php?s=&threadid=23429&highlight=climate+lights. I used the same Radio Shack "micro lamp" recommended in that thread. To replace the bulb you need to pull the small square black rubber bulb holder off the two metal prongs on the SRS indicator circuit board. With the rubber bulb holder removed you can extract the old bulb and its wire leads and then insert the new bulb in the bulb holder, being careful to route the wire leads so they will be in contact with the two prongs on the circuit board when you push the rubber bulb holder back in place. I purchased my new bulb at Radio Shack - #272-1092 - for $1.79. My local Honda parts counter didn't have replacement bulbs, but they did offer to sell me a new SRS indicator circuit board with bulb installed for $34.
6) Push the bulb holder with the new bulb down onto the two circuit prongs. Temporarily connect the SRS lighting harness to the SRS indicator circuit board and test the new bulb. It should light for around 6 seconds when the ignition is turned on. (Of course it won't go out after six seconds if the SRS unit discovers an error or if a previous error is stored in the SRS module's memory.)
7) Remove the yellow harness from the indicator circuit board and reinstall the indicator circuit board in the back of the instrument cluster. Install the white tab that locks the SRS indicator board into the back of the instrument cluster. Be careful not to tear the circuit sheet that runs the length of the back of the instrument cluster. Replace any other bulbs in the instrument cluster that you previously removed to facilitate handling the SRS indicator circuit board.
8) Reinstall the four screws holding the instrument cluster to the bulkhead and the three screws holding the cluster cover in place. Install the vent to the left of the cluster - just press it back in place.
That's it!
daneli
1996 Honda Odyssey
2000 Honda Odyssey
