Won't start turn ignition on does not crank gauges work battery is good already cleaned battery post and checked all fuses the voltage gauge in dash shows to be a little weak and the heater blower is not real strong but the battery is fully charged battery light in dash lights up also?

There could be a few potential causes for the dash gauges not working on your 2003 Honda Civic. Here are a few things to check:

1. Check the battery connections: Make sure the battery terminals are clean and tight. Loose or corroded connections can cause electrical issues.
2. Check the ground connections: Make sure the ground connections for the dash gauges are clean and tight. A bad ground connection can cause electrical issues.
3. Check the voltage regulator: The voltage regulator is responsible for regulating the voltage to the gauges. If it's faulty, it can cause the gauges to stop working.
4. Check the instrument cluster: It's possible that there's an issue with the instrument cluster itself. You may need to have it inspected by a mechanic.
5. Check for a blown fuse: Although you've checked the fuses already, it's possible that one of them has blown. Double-check the fuse for the instrument cluster to make sure it's not the issue.

If none of these solutions work, it's best to have a professional mechanic diagnose and repair the issue. They will be able to use specialized tools and equipment to identify the problem and find a solution.

Was original PCM dead? Has the 'new' PCM been working at all? The p1602 DTC is set when the battery voltage was detected as low or disconnected. Do the basics and check the battery terminals are clean and tight and that he engine has a good earth lead to the body. Check that battery voltage is 12.4v or higher. Check the fuses and relays. Clear the code and retry to start. If possible try the 'old' PCM if it was working before being swapped out.

If you mean the car won`t turn over then you could have a bad starter motor/solenoid. check voltage at the large wire terminal on the starter it should be battery voltage. then check voltage on the smaller wire terminal it should be battery voltage only when cranking. if not you will have to check out the wires for lose of voltage. make sure the starter has a good ground. if these are good then you have a bad starter that needs replacing.

Sounds like a problem in the ignition switch. When the gauges do not come on, how about the warning lights and the check engine light? If they don't turn on also, it may be a problem between the switch and the portion of the instrument panel fuse block that the switch sends power to in run or start-and then on to the dash for the gauges and warning lights.
You could check for power on the gauges fuse with key on. With the key in on position, all fuses in the instrument panel should have power to them. Check the fuses for power when the gauges do not come on. If no power in run, either the switch is bad, or however the switch sends power to those fuses (the ones called "hot in run or start") is not working. On some, the ignition switch's run wire trips a relay which sends power to the fuse panel. You would have to see a wiring diagram to see your set up. But it sounds like the problem is the switch or the wiring after it, not an engine sensor problem.

To check if a fuse has power, use a test light. Find a good ground for the test light under the dash, turn key to on, and use the needle probe of tester to probe the little indents on each end of the top of the fuse-these are test ports to check for power. A good fuse will light the tester on both ends of the fuse. A bad fuse (blown) will only light the tester on one end of the fuse-the metal strip inside the fuse has blown. Just check if all your fuses have power on them with the key on. Check them when the gauges don't work. IF no power, switch is bad or it is not turning that portion of the fuse panel on for some reason.

Check all your battery connections. Maybe not a good connection since your key doesn't turn on warning lights and gauges. See if your headlights work to verify a good battery connection.
Any chance you blew fuses? Like a maxi fuse for the ignition switch? Or for older vehicles that used a fusible link to connect battery power with the ignition switch. Keep diagnosing until you get power to the ignition switch (warning lights and gauges working with key ON).
Any chance your battery is totally discharged? Was the alternator working good when tested? If alternator quits working, engine and all electricals will run off the battery for a time until it is totally depleted, then will stall and won't have enough juice to even turn any lights on. Check battery voltage with a multi meter or voltmeter. A good, fully charged battery will show 12.6 volts. If under 12 volts, it may or may not have enough juice to start, but lights will still work some, though maybe very dim. .

SOUND LIKE DEAD BATTERY.HAVE BATTERY CHECKED AND REPLACED.MAKE SURE ALTERNATOR CHARGING BATTERY.WITH ENGINE IDLING BATTERY VOLTAGE OUTPUT AT BATTERY SHOULD BE 13.5 - 14.5 VOLTS. IF NOT CHECK ALTERNATOR BATTERY FEED WIRE AND VOLTAGE REGULATOR WIRES FOR DAMAGE OR LOOSE CONNECTIONS,CHECK ALTERNATOR FUSE AND MAKE SURE ALTERNATOR DRIVE BELT NOT LOOSE SLIPPING OR BROKEN.

IF BATTERY CABLES OLD THEY WILL CAUSE POOR GROUND HIGH RESISTANCE IN STARTER CIRCUIT CAUSING STARTER NOT TO CRANK ENGINE.CHECK TO SEE IF DASH LIGHTS AND GAUGES WORK WHEN YOU TURN ON IGNITION SWITCH IF NO CHECK IGNITION FUSES.IF FUSES OKAY IGNITION SWITCH IS OPEN NEED REPLACING.NOW IF BATTERY VOLTAGE IS 12.6 VOLTS, BATTERY CABLES GOOD AND IGNITION SWITCH AND FUSE OKAY. STARTER SOLENOID OR STARTER FAULTY.REMOVE STARTER TAKE TO ANY AUTO PARTS STORE THEY WILL TEST STARTER.TURN OFF RADIO BEFORE REMOVING NEGATIVE BATTERY SO YOU WONT LOCK OUT RADIO.

Checked Every fuse in the fuse box (no small task).This includes #4 - Power point Instrument Panel, #14 - Day time running lamps (auto lamps doesn't work nor does auto lock), #27 - ignition switch run feed, #35 - Instrument Cluster, #41 - Instrument Cluster, #42 - Delayed Accessory, #45 - Ignition switch run/start feed, #102 - Door locks body security module, #103 - Ignition switch, #110 - Ignition switch, & #116 - Ignition switch. But I also check all other ones as well, they all register OK. AC panel & radio work. Turn signals work. Mileage does not work, trip computer does. So, basically, everything works except auto head-lights, auto locks, and the dash cluster (no MPH, RPM, mileage display, Fuel, Temp, Tran Temp, and Oil Pressure).

Im guessing its the battery make sure all connections are tight .clean and free of acid build up,secondly make sure it is holding a charge and cranks out voltage.Next step check for blown fuses and very important check your fuse-able links and bad link will interrupt power to your dash,check that your getting power to ignition switch I hope this helps if not get back with me will get to the bottom of this

Check that the smaller wire going to battery positive terminal has a good connection. Check for blown fusible links under the hood and fuses in fuse panel.