OKI MC342, MC362 and MC562: fax cannot send or receive — Line Busy and Communication Error

Last Updated on 11.08.2026 by DriverNew

If an OKI MC342, MC362 or MC562 cannot send or receive faxes, reinstalling the printer driver usually does not help. A standard fax is transmitted over a telephone line, so first check the cable and the LINE connector, then the dialing method, PBX or VoIP settings and the reception mode on the MFP control panel.

This guide will also help with Line Busy, No Answer and Communication Error messages, no dial tone, inability to dial an outside number and unstable transmission through a router’s telephone port.

Which models this guide applies to

The standard fax function is available on the following models:

• OKI MC342dn and MC342dw;
• OKI MC362dn and MC362w;
• OKI MC562dn, MC562w and MC562dw;
• OKI ES5462 MFP and ES5462dw MFP;
• OKI MPS2731mc.

OKI MC332dn, MC352dn and ES3452 MFP look similar to the devices listed above, but they do not have the fax function discussed here. Do not look for LINE and TEL connectors on them and do not install a fax driver for another model.

The menu item names below are given in English. If another language is selected on the control panel, the menu locations remain the same, but the item names will be localized. An administrator password is required to access Admin Setup. The factory password for the listed models is aaaaaa, unless the device owner has changed it.

Before changing settings, determine the nature of the problem

Step 1. Check the LINE and TEL connectors

There are two similar telephone connectors on the back of the MFP, but they serve different purposes:

• LINE — telephone line input to the MFP;
• TEL — output for an additional analog telephone or answering machine.

1. You do not need to turn off the MFP for a normal cable check, but do not touch damaged wires or connectors.
2. Locate the cable coming from the telephone wall socket, analog PBX port, router or ATA gateway.
3. Make sure it is inserted into the LINE connector until it locks in place.
4. If an external telephone or answering machine is used, connect it to TEL.
5. Inspect the cable. Replace it if the plug is broken, the locking tab does not hold the connection or the cable has kinks or damage.

If the MFP is connected to an office telephone system

The LINE connector may only be connected to a compatible analog line or analog extension port of the PBX. A port intended for a proprietary digital system telephone may be electrically and protocol-incompatible with fax. If you do not know which type of port is being used, check with the specialist who maintains the PBX.

Step 2. Check the dial tone without the MFP

This test immediately distinguishes an MFP problem from a telephone line problem.

1. Disconnect the cable going to the MFP from LINE.
2. Connect this cable to a standard analog telephone.
3. Lift the handset and check for a dial tone.
4. Use the telephone to call a regular number.
5. Call this line from another telephone and make sure incoming calls work.
6. Reconnect the tested cable to LINE.

If there is no dial tone or outgoing or incoming calls do not work, contact the carrier, PBX administrator or check the router’s telephone port settings. OKI settings cannot restore an inactive line.

If a regular telephone works but the MFP does not dial, proceed to the dialing method and dial tone detection settings.

Step 3. Check tone or pulse dialing

Tone dialing is used by default. For most modern lines, PBXs and router telephone outputs, leave Tone selected. Pulse is required only for old lines that use pulse dialing.

1. Press the SETTING button on the MFP control panel.
2. Select Admin Setup and press OK.
3. Enter the administrator password, select Enter and press OK.
4. Open User Install.
5. Select MF(Tone)/DP(Pulse).
6. For a modern line, select Tone.
7. Select Pulse only if the carrier or PBX administrator has confirmed that pulse dialing is required.
8. Press OK and return to the main screen.

After changing the setting, send a test fax. Do not switch to Pulse simply because the first transmission failed: an incorrect dialing method completely prevents dialing.

Step 4. Send a simple test fax from the control panel

For the first test, do not use the phone book, group dialing, delayed transmission or the computer fax driver.

1. Place a one-page document face up in the ADF. If using the scanner glass, place the document face down.
2. Press the FAX button.
3. Select standard fax, not Internet Fax.
4. Open Direct Input.
5. Enter the recipient’s full number manually.
6. Check every digit.
7. Press START.
8. Wait for the attempt to finish and write down the message shown on the display.

Repeat the test with another known working fax. If transmission to one recipient succeeds but always fails with another, the local line and OKI modem are most likely working correctly.

How to distinguish a fax problem from a computer fax driver problem

If the document is sent successfully from the control panel but not from Windows, do not change the MFP telephone settings. The line has already been verified. In this case, separately check the installed fax driver, the selected queue and the connection between the computer and the MFP.

If Line Busy or No Answer appears

Line Busy does not always mean a physical fault. The MFP may have dialed an incorrect number, remained on the PBX internal line or incorrectly interpreted a service signal as busy.

1. Call the recipient’s number using a regular telephone.
2. If the number is actually busy, wait until the line is free. The MFP may perform an automatic redial.
3. If the call succeeds from the telephone, manually compare the number with the number entered on the MFP.
4. If the OKI phone book is used, repeat the test using Direct Input. This can reveal an error in the saved entry.
5. When connected through a PBX, check the outside-line prefix and the pause after it.
6. If the message appears immediately after dialing begins, check PBX Line and Dial Tone Detection.

No Answer means that the connection did not proceed to fax communication. Ask the recipient to check whether their fax machine is turned on, whether the correct reception mode is selected and whether paper is available. If a person answers by voice, ask them to start fax reception manually.

Configure automatic redialing

Automatic redialing is useful for a genuine busy signal, no answer and a temporary communication error.

1. Press SETTING.
2. Open Admin Setup → Fax Setup → Other Settings.
3. Select Redial Tries.
4. Set the number of retry attempts from 0 to 9.
5. Open Redial Interval.
6. Set the interval from 1 to 5 minutes.
7. Save the changes.

Redialing does not fix an incorrect number, a missing PBX prefix or an inactive line. Correct the underlying cause first.

If the fax is connected through an office PBX

When connected to an analog PBX extension, a digit is usually required to access an outside line, for example 0 or 9. After this digit, the MFP must wait until the PBX provides an outside line.

Enable PBX Line

1. Press SETTING.
2. Open Admin Setup and enter the password.
3. Select Fax Setup → Fax Setting.
4. Open PBX Line.
5. Select ON.
6. Press OK.

Save the outside-line prefix

1. Open SETTING → Admin Setup → Fax Setup → Other Settings.
2. Select Prefix.
3. Enter the digit or sequence used to access an outside line.
4. Save the value by pressing OK.
5. When entering the recipient’s number, use the PreFix command if it is displayed on the direct input screen.

Add a pause after the prefix

If the PBX does not provide a line immediately, enter the prefix, then press Pause and only then enter the number. One pause lasts approximately two seconds; if necessary, you can add several pauses.

For example, if 9 is used to access an outside line, the dialing sequence should look like this:

9 → Pause → recipient number

If the pause is too short, the first digits of the number are sent before the outside line becomes available. If it is too long, it usually only delays the call.

If the MFP does not recognize the PBX dial tone

1. Make sure a regular telephone connected through the same PBX port can make outside calls.
2. Check that PBX Line is enabled and the prefix is set correctly.
3. Open SETTING → Admin Setup → User Install → Dial Tone Detection.
4. If dialing does not begin because of a non-standard PBX dial tone, set it to OFF.
5. Send a test fax.

Disabling dial tone detection does not create a telephone line. The MFP simply starts dialing without waiting for a recognizable signal. Do not disable this check if the reason for the missing dial tone has not yet been identified.

If Communication Error appears

Communication Error means that fax communication started or was requested but did not complete. The cause may be the local line, remote device, interference or audio conversion in an IP network.

1. Retry the transmission once. A temporary disturbance may not occur again.
2. Check the number and call the recipient by voice.
3. Send the same page to another recipient.
4. If the second recipient receives the document, ask the first recipient to check their fax and line.
5. If the error occurs with all recipients, check the connection cable and eliminate any telephones connected in parallel.
6. If the line passes through a router, ATA or VoIP, disable Super G3 and reduce the modem speed using the instructions below.
7. Check the transmission report instead of judging the result only by the brief message on the display.

If the error occurs only at a certain time, check the line quality at another time of day. Packet loss and VoIP connection congestion can affect fax communication even when voice calls remain acceptable.

Configure fax for VoIP, IP telephony and a router telephone port

A standard fax cannot be transmitted through the MFP’s Ethernet network connector. The telephone cable must run from an analog PHONE, TEL or FXS port on the router or ATA gateway to the LINE connector on the OKI.

1. Check that the router port is activated by the carrier and that a regular telephone connected to it can make and receive calls.
2. Do not connect the OKI to a LAN network connector instead of the telephone line.
3. Ask the carrier whether fax and the T.38 protocol are supported.
4. If the carrier allows the voice codec to be selected, fax usually requires the uncompressed G.711 codec. The specific setting must be confirmed by the carrier.
5. Disable functions that alter the line’s audio signal if the carrier provides such settings: silence suppression, some bandwidth-saving modes and voice optimization.
6. After checking the connection, change OKI settings one at a time.

Disable Super G3

1. Press SETTING.
2. Open Admin Setup → User Install.
3. Select Super G3.
4. Set it to OFF. The MFP will use standard G3 mode.
5. Save the setting and retry transmission.

Reduce the modem speed

The factory setting of 33.6 Kbps provides fast transmission but places higher demands on the line. For IP telephony, test 14.4 Kbps, and if errors continue, 9.6 Kbps.

1. Press SETTING.
2. Open Admin Setup → Fax Setup → Fax Setting.
3. Select H/Modem Rate (For Tx).
4. Set 14.4 Kbps.
5. Select H/Modem Rate (For Rx).
6. Also set 14.4 Kbps.
7. Test sending and receiving.
8. If Communication Error remains, set both transmission and reception to 9.6 Kbps and repeat the test.

Change the transmission and reception speeds together if problems occur in both directions. If only sending does not work, you can first reduce only For Tx; if only receiving does not work, reduce For Rx.

Do not disable ECM unless necessary

ECM Mode detects and corrects errors caused by noise on the telephone line. Under normal conditions and for most problems, it should remain enabled.

A brief test with ECM OFF is appropriate only as a final diagnostic measure if the VoIP carrier cannot provide compatible transmission and errors remain after disabling Super G3 and reducing the speed. With ECM disabled, the document may be received with missing data or distortion.

1. Open SETTING → Admin Setup → Fax Setup → Other Settings.
2. Select ECM Mode.
3. For normal operation, use ON.
4. If performing a diagnostic test, temporarily select OFF, send one page and evaluate the result.
5. If there is no improvement, restore ON.

If the OKI sends but does not receive faxes

Successful transmission confirms that the line is connected to LINE and the MFP can dial numbers. In this case, first check the reception mode.

Select the appropriate Reception Mode

1. Press SETTING.
2. Open Admin Setup and enter the password.
3. Select User Install → Reception Mode.
4. Select a mode from the table below.
5. Press OK and return to the main screen.

If faxes must be received without user intervention, do not select Tel Ready Mode. For a dedicated fax line, select Fax Ready Mode.

Configure the ring response time

If the response time is too short, there is not enough time to answer the external telephone. If it is too long, the sending fax may stop waiting.

1. Open SETTING → Admin Setup → Fax Setup → Other Settings.
2. Select Ring Response.
3. Set an appropriate number of rings or waiting time.
4. If caller ID is used on the line and the fax does not answer, test 10 seconds, 15 seconds or 20 seconds.
5. Call the line and check the MFP’s behavior.

If an answering machine is used

1. Connect the answering machine or telephone with an answering machine only to TEL.
2. Select Ans/Fax Ready Mode.
3. Keep the greeting short and avoid long pauses.
4. Configure the answering machine to answer before the call is disconnected by the carrier or sending fax.
5. Test a voice call and an incoming fax separately.

Some answering machines and sending fax machines may not detect each other reliably. If reception does not start, temporarily disconnect the answering machine, select Fax Ready Mode and repeat the test. Successful reception confirms that the problem is related to interaction between the devices rather than the OKI modem.

If the fax is received but does not print

An illuminated DATA IN MEMORY indicator means that data is stored in memory. A received fax may not print because suitable paper is unavailable, there is a paper jam, a cover is open, there is a consumables error or another condition is preventing printing.

1. Read the message on the display and correct the indicated error.
2. Load a supported paper size into the configured tray.
3. Check that the paper size and type are registered correctly in SETTING → Paper Setup.
4. Remove jammed paper if a jam code is displayed.
5. Close all covers and trays.
6. Check toner and image drum messages.
7. Wait for the stored fax to print automatically after the MFP returns to the ready state.

If the memory is full, new incoming faxes may be rejected. Finish printing stored documents, cancel unnecessary delayed jobs and ask the sender to retransmit the fax.

How to obtain detailed error information

The brief Communication Error message does not indicate at which stage the transmission was interrupted. Use the confirmation report and fax log for troubleshooting.

Enable a report for the next transmission

1. Press FAX and open the standard fax screen.
2. Select Fax Functions.
3. Open Transmit Confirmation Report.
4. Select ON.
5. Send the test document.
6. Keep the printed report.

Print the transmission and reception log

1. Press SETTING.
2. Select Reports → Fax.
3. Open Fax Tx/Rx Log.
4. Enter the administrator password if requested.
5. Select Yes to print.

The log contains the results of the most recent sent and received jobs. Compare the time, recipient number and result of several attempts. A persistent error with only one number points to the remote side or a specific communication route; errors with all numbers point to the local line or settings.

If faxes work only intermittently

1. Eliminate telephone splitters, extension cables and damaged cables.
2. Make sure no one lifts a parallel telephone handset during transmission.
3. Test operation with two different recipients.
4. For VoIP, disable Super G3 and set the speed to 14.4 Kbps.
5. If errors continue, test 9.6 Kbps.
6. Leave ECM enabled if testing with it disabled did not produce a clear improvement.
7. Provide the carrier with the time of the error and the log result so they can check the telephone route.

Do not randomly change Service Bit, Attenuator, pulse dialing coefficients or the country code. These values are related to regional and service line parameters. Incorrect settings can introduce additional errors and make troubleshooting more difficult.

When the problem is outside the MFP

Contact the carrier or PBX administrator if a regular telephone does not receive a dial tone, calls are interrupted, the VoIP port does not support fax, a digital system telephone port is being used or communication loss occurs at the same time on different devices.

The MFP itself may require service if a tested analog line works with another fax machine, but the OKI does not detect it, does not respond to incoming calls in any mode and cannot send documents to several recipients after Tone, PBX Line, Super G3 and modem speed have been checked. Before requesting service, save the Fax Tx/Rx Log, the exact message text, information about the line type and the results of tests with two numbers.