My 94 Nissan Altima ECU is giving code #21. This is for Ignition signal. Haynes manual says, "See dealer". It is also coding #11 - camshaft sensor.

do you hear your fuel pump kick on when you you turn the key?

get a HAYNES repair manual, tells you what all sensors do ! the crankshaft sensor sends info to the SBEC, reguarding engine crankshaft position. the camshaft sensor reads camshaft position, sends a coded signal to the SBEC, which uses this info to determine whether the fuel injectors and ignition coils are correctly synchronized !

Try the crankshaft sensor

rear of both cylinder heads.however these are not cam sensor codes.these are intake timing control codes and since you have set codes for both banks i would suspect a low oil level or an oil pressure issue is causing them.sensor codes would be 340 and 345.

service manual.
Code Description Possible Cause
0 ECU / ECU signal No signal to ECU
1 Oxygen sensor circuit Oxygen sensor or circuit, ECU
2 Oxygen sensor circuit Oxygen sensor or circuit, ECU
3 MAP sensor circuit Map sensor circuit
4 CKP sensor / engine speed (RPM) Crank angle sensor or circuit, ECU
sensor
5 MAP sensor circuit MAP sensor or circuit, mechanical
problem
6 ECT sensor circuit ECT sensor or circuit, automatic
transaxle control unit
7 TPS / Angle Sensor TPS sensor or circuit, automatic
transaxle control unit
8 CKP sensor / engine speed (RPM) Crank angle sensor or circuit, ECU
sensor
9 CMP sensor CMP sensor or circuit
10 IAT sensor IAT sensor or circuit
11 Idle Mixture Adjuster Sensor Idle mixture adjuster sensor or
circuit
12 EGR system fault No EGR action, faulty EGR valve
13 BARO sensor circuit BARO sensor or circuit
14 Idle Air Control valve circuit / ECU Open or shorted out ignition signal
circuit / No signal to ECU
15 Ignition Output signal Open or shorted ignition output
signal circuit
16 Fuel Injector Circuit Open or shorted fuel injector
circuit
17 VSS circuit VSS sensor or circuit
18 Ignition Timing Adjuster Open or shorted signal circuit
19 A/T Lock-up control solenoid Open or shorted signal circuit,
Lock-up control solenoid lock-up solenoid
20 Electrical Load Detector / Sensor Electrical load detector or circuit
Honda/Acura
Fault Code Definitions (21 - 59)
Chapter 3 22
Code Description Possible Cause
21 Spool Solenoid Valve Open or shorted signal circuit,
spool solenoid valve
22 Valve Timing Electronic Oil Open or shorted signal circuit,
pressure switch valve timing oil pressure switch
23 Knock sensor circuit Knock sensor or circuit
30 AT / ECU communication signal A AT control unit, ECU
31 AT / ECU communication signal B AT control unit, ECU
35 Traction control / ECU / signal Traction control module, ECU
36 Traction control / ECU / signal Traction control module, ECU
41 Oxygen sensor heater - left side Oxygen sensor / heater or circuit
42 Oxygen sensor heater - right side Oxygen sensor / heater or circuit
43 Fuel Supply system - left side Oxygen sensor or circuit, fuel
system
44 Fuel Supply system - right side Oxygen sensor or circuit, fuel
system
45 Fuel metering - left side Injector control circuit, incorrect
fuel metering
46 Fuel metering - right side Injector control circuit, incorrect
fuel metering
48 Heated oxygen sensor Oxygen sensor or circuit
53 Right Knock Sensor Right knock sensor or circuit
54 CKP sensor 2 CKP sensor 2 or circuit
59 CMP sensor 2 CMP sensor 2 or circuit

They may be right. I cannot find the part. here is what the manual says:

REMOVAL & INSTALLATION The camshaft position sensor is located inside the distributor. On some distributors, the camshaft position sensor is not serviceable (replacement parts may not be available separately). If the camshaft position sensor is serviceable, use the following procedure.

1. Remove the distributor cap and wires.
2. Remove the rotor.
3. Remove the camshaft position sensor cap.
4. Remove the camshaft position sensor mounting screws.
5. Carefully remove the camshaft position sensor.

To install:

1. Position the camshaft position sensor in the distributor and tighten the mounting screws securely.
2. Install the camshaft position sensor cap.
3. Install the rotor.
4. Install the distributor cap and wires.

Replace the O2 Sensor, reset the ECU, and subject solve.

Good luck.

did you get any related engine trouble codes? well for no start it could be a faulty cranskshaft sensor (pos), camshaft sensor (phase) or faulty fuel pump.
check for busted fuse.
check your ignition power and ground.
check power and signal for injectors.

hope this ideas would help.

(11)--"A"camshaft position timing over-advanced or system performance bank 1++ ( 21)-- "A"same as above but bank 2 ++(24)--"B" same as above but bank 2=== check ur wiring and connections to ur oil control valve and solenoid and power control module also check ur v v t/v c t variable valve timing /variable camshaft timing circuits

In the kit there are two sensor that look identical. The one for the crankshaft has a white paint mark on it near the bolt hole. Make sure that it is in the right location.