Timing belt comes loose when reaching vtec and then the engine won't start.

Whenever I hear the statement, "shut off without any warning and will not start", the first thing I think of is the timing belt. It is often a forgotten maintenance item and when it finally fails, the results are immediate and dramatic. If the engine turns over very fast (faster than normal), and won't start, you can bet its a timing belt. Unfortunately, the VTec engine is an interference engine. This means that if the timing belt breaks, the results will be internal engine damage since the piston/valve clearances are no longer maintained by the belt. Simply replacing the belt, which many refuse to do because of the cost involved, will no longer solve the issue. Now, the costs are doubled since the cylinder head must be repaired or replaced, depending upon the amount of damage. There is even the possibility of damaged pistons. I hope for your sake this is not the issue, but if the car has more than 80K miles and the timing belt has never been replaced, it is the most likely problem.

problem could be with the vtec. not varying timing .

What is wrong is that you changed a part

You failed to follow any trouble charts because
you have none

The sensor was most likely okey & just doing it's
job of reporting a fault

You could have a mechanical problem such as a timing
belt issue or worn VVT Actuators on the end of the cames

You have to diagnose code related issues & then find out
why a sensor reported as it did

Even if you scoped the sensor you would most likely
assume it was bad,not so,have to keep thinking why the
data was bad

You need professional tools & look at several pieces of data
overlayed on a big sceen at one time

Repair shop or dealer for that issue

Check and see if timing belt jumped . The belt may be missing a couple of teeth

from autozone.com:
1990-95 4-Cylinder Accord and 1992-95 Prelude

1. Disconnect the negative battery cable.
2. Turn the engine to align the timing marks and set cylinder No. 1 to TDC on the compression stroke. Once in this position, the engine must NOT be turned or disturbed. On DOHC Preludes without VTEC, hold each of the camshafts in the TDC position by inserting 5mm diameter punches into the alignment holes just behind each cam pulley.
3. Remove the splash shield from below the engine.
4. Drain the engine coolant. Use a clean container; cap or cover the container and wipe up spillage.
5. Unplug the electrical connector at the cruise control actuator, then remove the actuator. Don't disconnect the cable; simply move the actuator out of the work area.
6. Remove the belt from the power steering pump. Remove the mounting bolts for the pump. Without disconnecting the hoses, move the pump out of the way.
7. Unplug the alternator wiring and connectors; remove the engine wiring harness from the valve cover.
8. Loosen the adjusting and mounting bolts for the alternator and/or compressor. Remove the drive belt(s).
9. Remove the valve cover.
10. Remove the side engine mount support bracket, if equipped.
11. Remove the upper timing belt cover.
12. Support the engine with a floor jack on the oil pan (use a cushion between the jack and pan). Tension the jack so that it is just supporting the engine but not lifting it.
13. Remove the side engine mount.
14. Remove the dipstick and dipstick tube.
15. Remove the crankshaft pulley bolt and remove the crankshaft pulley.

This bolt is one of the tightest on the entire car. The pulley must be held in place while the bolt is loosened. One trick is to wrap an old drive belt around the pulley to hold it steady-don't try this with a belt that is to go back on the car; it will be stretched or damaged.

1. If necessary for additional clearance to remove the lower timing belt cover, remove the two rear bolts from the center beam. Slowly lower the jack and the engine until the clearance is gained.
2. Remove the rubber seal from around the belt tension adjusting nut (do not loosen the nut). Remove the lower timing belt cover.
3. On all models except Prelude with VTEC, lock the timing belt adjuster arm in place using one of the lower cover (6 x 1mm) mounting bolts.

Fig. 10: On all engines except VTEC, the belt adjuster arm must be locked in place using one of the lower cover mounting bolts
There are two belts in this system; the one running to the camshaft pulley is the timing belt. The other, shorter one drives the balance shaft and is referred to as the balancer belt or timing balancer belt. Use a piece of chalk or a marker to place an identifying arrow on the belts. The arrow can identify the direction of rotation or the outer edge of the belts. The belts must be reinstalled so it moves in the same direction. Protect the belts from oil, coolant, etc. It's an even better idea to replace the belts at this point.

1. Loosen the timing belt adjustment nut. Push on the tensioner to relieve tension from the balancer belt, then tighten the nut. Remove the balancer belt.
2. On all models except Prelude with VTEC, loosen the lockbolt installed earlier and the adjusting nut. Push on the tensioner to release the timing belt, then tighten the nut. Carefully remove the timing belt. On Prelude VTEC models, remove the timing belt from the pulleys, then remove the bolts securing the auto-tensioner. Remove the auto-tensioner from the engine.

To install:

1. Check the position of the timing marks. The timing pointer must be perfectly aligned with the TDC (white mark) on the flywheel or flex-plate; the camshaft pulley must be aligned so that the word UP is at the top of the pulley and the marks on the edge of the pulley are aligned with the surfaces of the head. Additionally, the face of the front timing balancer pulley has a mark which must be aligned with the notch on the oil pump body. This pulley is the one to the left crank when viewed from the pulley end.
2. Fit the timing belt over the pulleys and tensioner. On DOHC engines without VTEC, remove the 5mm pin punches from behind the cam pulleys.
3. Except Prelude VTEC models:
   1. Temporarily install the crank pulley and bolt.
   2. Loosen the tensioner adjusting nut 1 turn, then tighten it. Rotate the crankshaft counterclockwise until the camshaft pulley has moved 3 teeth to create tension on the belt. Loosen the nut again, then tighten it to 33 ft. lbs. (45 Nm).

Always rotate the crankshaft counterclockwise when viewed from the pulley end. Rotating it clockwise will cause improper adjustment and possible damage.

1. On Prelude VTEC models:
   1. Hold the auto-tensioner with the maintenance bolt facing up. Loosen and remove the bolt.

Handle the tensioner carefully so the oil inside does not spill or leak. Replenish with clean engine oil if any does leak. Total capacity is1/4fl. oz. (8 ml).

1. Make sure all timing marks are positioned correctly (as described earlier).
2. Align the rear timing balancer pulley (to the right of the crank pulley) using a 6x100mm bolt or rod. Mark the bolt or rod at a point 2.913 in. (74mm) from the end. Remove the bolt from the maintenance hole on the side of the block; insert the rod into the hole. Align the 74mm mark with the face of the hole. This pin will hold the shaft in place during installation.
3. Loosen the tensioner adjusting nut and verify that the timing balancer belt adjuster moves freely.

Fig. 13: The balancer shaft must be held in position during timing belt installation

1. Fit the balancer belt over the pulleys. Remove the bolt or rod from the maintenance hole.
2. Temporarily install the crank pulley. Rotate the engine one turn counterclockwise, then tighten the tensioner adjusting nut to 33 ft. lbs. (45 Nm). Double check the positions of the timing marks and make sure they still line up. If not remove the belts and repeat the procedures.

Both belt adjusters are spring-loaded to properly tension the belts. Do not apply any additional pressure to the pulleys or tensioners while performing the adjustment.

1. Remove the crank pulley. Remove the lockbolt installed earlier on the timing belt adjuster arm. Install the maintenance bolt with a new washer. Tighten it to 22 ft. lbs. (30 Nm).
2. Install the lower cover, making certain the rubber seals are in place and correctly located. Tighten the retaining bolts to 9 ft. lbs. (12 Nm).
3. If applicable, raise the lower beam and engine into place. Install the rear bolts for the lower beam. Tighten them to 28 ft. lbs. (39 Nm) on 1990-91 Accords, 37 ft. lbs. (50 Nm) on 1992-95 Accords and 43 ft. lbs. (60 Nm) on 1992-95 Preludes.
4. Install the key on the crankshaft and install the crankshaft pulley. Apply oil to the bolt threads and tighten it to the following: 1991-93 Accord: 159 ft. lbs. (220 Nm)

1. Install the dipstick tube and dipstick.
2. Install the side engine mount (refer to engine removal and installation for procedures). Remove the jack from under the engine.
3. Install the upper belt cover.
4. Install the side engine mount support bracket if it was removed.
5. Install the valve cover.
6. Install the compressor and/or alternator drive belt; adjust the tension.
7. Route the wiring harness over the valve cover and connect the wiring to the alternator.
8. Install the power steering pump and install the belt.
9. Reinstall the cruise control actuator. Connect the vacuum hose and the electrical connector.
10. Double check all installation items, paying particular attention to loose hoses or hanging wires, untightened nuts, poor routing of hoses and wires (too tight or rubbing) and tools left in the engine area.
11. Refill the engine coolant.
12. Install the splash shield under the engine.
13. Connect the negative battery cable.
14. Start the engine, allowing it to idle. Check for any signs of leakage or any sound of the belts rubbing or binding.

http://www.vidzshare.net/videos/EmasxgJdXJ8/how-to-change-timing-belt-in-a-vtec-honda-accord.html

Go to the above link and get a video explanation of how to replace timing belt in all accord with vtec engine...

It has a timing belt

reset the ecu pull #6 fuse 15a for 10 msec. check oil level fill if needed. start engine hold at 3 grand for at least 2 sec road test if still comes back 1259 repeat 2 times. If it is gone it is intermit problem check for loose terminals at VTEC solenoid vavle oil pressure switch and the ECM/PCM. If you still have the code turn ignition off remove resonator disconnect the VTEC oil pressure switch 2p connector check for contnuity between VTEC oilpress switch terminals 1 and 2 if none replace the oil pressure switch. if yes measure voltage between ECM/PCM connector B9 and body ground. Voltage? repair open wire between B9 and the oil pressure switch. If no than the ECM/PCM will need to be checked for the latest software and reprogrammed to be further diaged. This will only be able to bedone at the dealer.

Please rate me solved...thanks!
DTC P1259: VTEC SYSTEM MALFUNCTION
1. Perform PCM reset procedure. See SELF-DIAGNOSTICS - INTRODUCTION article. Start engine
and run at 3000 RPM with no loads and transmission in Park or Neutral until radiator fan comes on. Road
test vehicle. Accelerate in 1st gear to an engine speed over 4000 RPM and hold that engine speed for at
least 2 seconds. If DTC P1259 is not indicated during first road test, repeat road test 2 more times. If DTC
P1259 is indicated, go to next step. If DTC P1259 is not indicated, problem is intermittent. System is
okay at this time. Check for poor connections or loose wires at VTEC solenoid valve connector and PCM.
See ENGINE PERFORMANCE WIRING DIAGRAMS article. Repair as necessary.
2. Turn ignition off. Disconnect VTEC pressure switch 2-pin connector. Check for continuity between
VTEC pressure switch terminals. If continuity exists, go to next step. If continuity does not exist, replace
VTEC pressure switch.
3. Turn ignition on. Measure voltage between ground and VTEC pressure switch harness connector terminal
No. 2 (Blue/Black wire). If about 12 volts exist, go to next step. If about 12 volts do not exist, check for
an open or short in Blue/Black wire between VTEC pressure switch and PCM 31-pin connector "C"
terminal No. 10. Repair as necessary. If wire is okay, substitute a known-good PCM and recheck. See
SUBSTITUTING PCM in SELF-DIAGNOSTICS - INTRODUCTION article. If symptom or problem
goes away, replace original PCM.
4. Measure voltage between VTEC pressure switch harness connector terminals. If battery voltage exists, go
to next step. If battery voltage does not exist, repair open in Brown/Black wire between VTEC pressure
switch and ground connector located on left side of engine, under throttle plate, between end of radiator
hose and cooling fan switch. See ENGINE PERFORMANCE WIRING DIAGRAMS article. If wire is
okay , substitute a known-good PCM and recheck. See SUBSTITUTING PCM in SELFDIAGNOSTICS
- INTRODUCTION article. If symptom or problem goes away, replace original PCM.
5. Turn ignition off. Disconnect VTEC solenoid valve connector. Measure resistance between ground and
VTEC solenoid valve connector. See ENGINE PERFORMANCE WIRING DIAGRAMS article. If
resistance is 14-30 ohms, go to next step. If resistance is not 14-30 ohms, replace VTEC solenoid valve.
6. Remove VTEC pressure switch and install Pressure Gauge Adaptor (07NAJ-P07010A) and A/T Low
Pressure Gauge (07406-0070300). Reinstall VTEC pressure switch into adaptor. Connect tachometer.
Start engine and with no loads and transmission in Park or Neutral until radiator fan comes on. Because
engine is running with no load, oil pressure must be checked within one minute. Check oil pressure at
engine speeds of 1000, 2000 and 3000 RPM. If oil pressure is less than 7 psi (48 kPa), go to next step. If
oil pressure is 7 psi (48 kPa) or more, check VTEC solenoid valve. See SYSTEM & COMPONENT
TESTING article.
7. Turn ignition off. Disconnect VTEC solenoid valve connector. Connect a fused jumper wire between
battery voltage and VTEC solenoid valve connector. Start engine and check oil pressure at 3000 RPM. If
oil pressure is more than 57 psi (393 kPa), go to next step. If oil pressure is 57 psi (393 kPa) or less,
check VTEC solenoid valve. See SYSTEM & COMPONENT TESTING article.
8. Ensure jumper wire is still connected to VTEC solenoid valve connector. Start engine and allow it to idle.
Set engine speed to more than 4000 RPM and measure voltage between ground and PCM 31-pin
connector "C" terminal No. 10 (Blue/Black wire). See ENGINE PERFORMANCE WIRING
DIAGRAMS article. If battery voltage exists, go to next step. If battery voltage does not exist, replace
VTEC pressure switch.
9. Turn ignition off and disconnect jumper wire. Check for continuity between VTEC solenoid valve
harness connector and PCM 25-pin connector "B" terminal No. 12 (Green/Yellow wire). See Fig. 2 . See
ENGINE PERFORMANCE WIRING DIAGRAMS article. If continuity exists, go to next step. If
continuity does not exist, repair open in Green/Yellow wire between VTEC solenoid valve connector and
PCM 25-pin connector "B" terminal No. 12.
10. Check for continuity between ground and VTEC solenoid valve connector. See ENGINE
PERFORMANCE WIRING DIAGRAMS article. If continuity exists, repair short in Green/Yellow
wire between VTEC solenoid valve connector and PCM 25-pin connector "B" terminal No. 12. If
continuity does not exist, substitute a known-good PCM and recheck. See SUBSTITUTING PCM in
SELF-DIAGNOSTICS - INTRODUCTION article. If symptom or problem goes away, replace original
PCM