Most of the commands I send to SIM800C module returns ERROR message to me.

For example:

If I sent AT+CSQ, it returns an expected response.

One of the basics commands that doesn't worked for me is the AT+CPIN? PIN checking command.

In the datasheet, I don't even can find the possible cause for this error.

Another information I have:

Among many explanations for the problem, I found one, and I don't remember which was, that said to send a command to expand ERROR in details. As result from AT+CPIN?, I received a error that corresponds to "no card inserted" and I don't know why. The SIM card works fine, I have tested on my phone.

The SIM card is not detected by module. I measured the voltage in the card bus and I have 0 volts. I don't know it is the cause or the consequence for bad functioning, not even it is related to this main problem of this question.

This is my circuit:

SIM800 circuit sheet

  • 1
    Can you elaborate a bit on your setup? What is connected to what? Who sends the commands, etc...
    – Helmar
    Feb 7, 2017 at 7:33
  • It is you who designed and built the hardware around the module or you bought a SIM800 breakout board? In the first case please share your schematics in second share a link about the breakout board. Also verify with phone that the SIM card is alright and detectable by other devices. Feb 7, 2017 at 8:11
  • SIM card holder footprint is double checked? So the correct pins are connected? Feb 7, 2017 at 11:37
  • 1
    I found here (microchip.com/forums/FindPost/621998) a way to check for the VDD signals on the SIM card. And it sends 1.8 and 3.3V signals correctly. In that post, @rpg7 says the card responds with a reset pulse from card reset pin. I could read ~15ms reset pulse with a scope. So it seams to work fine.
    – luigiesn
    Feb 7, 2017 at 12:26
  • 1
    There is no noise on the bus. It maybe on low voltage scales, but I'm sure is nothing significative for the bus standards.
    – luigiesn
    Feb 7, 2017 at 20:28

2 Answers 2


The problem was bad contacting between SIM card contact block and the board. The problem was difficult to find because when I touched the terminal for measurement it makes pressure to the board, the contact happens and the problem couldn't be observed.

I made a check list for resolution:

  • Is SIM card working?
  • Are voltages on card correct?
  • Can bus signals be seen in a scope?
  • Is SIM card contacts block footprint correct?
  • Is card in the correct position?
  • Are SIM card VDD and GND both connected?

After eliminated most of all those questions the only possibility was the last one. Fact! I touched GND in the card holder very very delicately and the problem was there, a Heisenbug.

I hope this answer and checklist help a lot, because information about this kind of problem is very difficult to find.


You can enable extended error reporting, by sending AT+CERR.

Different devices will give different informaiton, but you should at least get some diagnostic help/hint.

For instance, this page says

AT+CEER - Extended error report

Execution command causes the TA to return one or more lines of information text , determined by the ME manufacturer, which should offer the user of the TA an extended report of the reason for

  • the failure in the last unsuccessful call setup (originating or answering)
  • or in-call modification,
  • the last call release,
  • the last unsuccessful GPRS attach or unsuccessful PDP context activation, the last GPRS detach or PDP context deactivation.

Typically, the text will consist of a single line containing the cause information given by GSM network in textual format.

Defined values

<report>: the total number of characters, including line terminators, in the information text shall not exceed 2041 characters. Text shall not contain the sequence 0 or OK

  • 2
    I performed this command and the only I receive is +CEER: No cause. Check my edits in my question. I put there some other information about the error.
    – luigiesn
    Feb 7, 2017 at 11:33

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