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I have been having intermittent trouble with my car detecting the key for starting. Key not detected message on dash and I have to insert the key to start. I've scanned the KEYLESS GO system multiple times with no DTCs reported, but today I finally got a DTC to report:
DTC: 9A5213
Description: HF antenna 'KEYLESS GO' has a malfunction. There is an open circuit.
Status: Current and Stored
Unfortunately, none of the WIS descriptions for the KEYLESS GO system show an "HF antenna".
Question: Is the "interior antenna" A2/61 shown below the HF antenna identified by the DTC?
Two bulletins indicate KG CU (n69/5) may need software update. Depending on build date 049924 may apply, 060558 seems applicable. There are 5 antennas, key seems to be recognized up to CU but not passed along to EIS requiring key insert.
Update. After extensive testing, I found that 3 of the 4 HF antennas in my car had deteriorated to a point where it appears they don't effectively picking up the Keyless GO signals from the key.
Specifics: There are 4 passive HF antennas in the w212 for Keyless GO - these are shown as A2/35, A2/39, A2/41 and A2/61 in the KG.pdf attachment. All four are have the same part number A2078200075 - at least in my 2012. From my research these are basically a capacitor in series with an inductor configured to resonate at the Keyless Go Frequency (315 MHz). One is located below the radio controls (above the climate control), one is attached to the inside of each rear door, and the other is on the floor of the trunk. There is also an powered AM/FM/Keyless GO amplifier (A2/18) attached to the roof near the rear window (A2128703889) but does not appear to be an issue in my car.
Given the error and my symptoms, I purchased a used replacement antenna. Testing the antenna using a DMM showing a resistance that changed over time and a capacitance tests showed 325 nF. Testing the 4 antenna capacitance readings (from the detached Keyless-GO module connectors) showed 58 nF (interior front), 46 nF (left door), 61 nF (right door) and 334 nF (trunk). At that point I wasn't sure if these antennas should be in the 325 nF range or in the 55 nF range, so I ordered a brand new antenna from the dealership. It tested at 325nF. I now surmise the 3 low antennas have leaking capacitors internally. plan to replace the 3 antennas that tested low with 3 in the 325 nF range - after buying another used one on eBay and testing it.
Well this is embarrassing, but the I don't want to leave a misleading post on the forum.
The passive antennas - part number A2078200075 - that I had thought were bad all tested good when capacitance was tested at the antennas. My initial capacitance tests were all taken from the wiring at the module which was easiest to get to. The extended wiring apparently affected the readings.
Replacing the AM/FM/Keyless GO amplifier (part A2/18 in the figure) attached to the roof near the rear window (rear portion of headliner pops out to expose it - part number A2128703889) immediately restored the system to its original efficiency.
01-26-2020, 04:51 PM
